Related
Sounds a little stupid, but I need help on my toString() method and it is very irking.
I tried looking up online because the toString is the one where it is screwing up and "not finding Kid constructor #2" even though it is there and I would even do something else and it doesn't work.
Ok that was a lot so here is my code:
import java.util.*;
class Kid {
String name;
double height;
GregorianCalendar bDay;
public Kid () {
this.name = "HEAD";
this.height = 1;
this.bDay = new GregorianCalendar(1111,1,1);
}
public Kid (String n, double h, String date) {
// method that toString() can't find somehow
StringTokenizer st = new StringTokenizer(date, "/", true);
n = this.name;
h = this.height;
}
public String toString() {
return Kid(this.name, this.height, this.bDay);
}
} //end class
Ok So my toString above (I know, my third parameter is off, should be a String) is off. If I hardcode a value in for the third thing it goes haywire and says it can't find this (up above). So how can I get the date and break it up?
Class calling this is below
class Driver {
public static void main (String[] args) {
Kid kid1 = new Kid("Lexie", 2.6, "11/5/2009");
System.out.println(kid1.toString());
} //end main method
} //end class
I tried researching multiple constructors and it really didn't help.
I tried researching toString() methods, and tried using previous toString() methods logic that I created previous but this is brand new so it never worked.
Help?
The toString is supposed to return a String.
public String toString() {
return "Name: '" + this.name + "', Height: '" + this.height + "', Birthday: '" + this.bDay + "'";
}
I suggest you make use of your IDE's features to generate the toString method. Don't hand-code it.
For instance, Eclipse can do so if you simply right-click on the source code and select Source > Generate toString
Java toString() method
If you want to represent any object as a string, toString() method comes into existence.
The toString() method returns the string representation of the object.
If you print any object, java compiler internally invokes the toString() method on the object. So overriding the toString() method, returns the desired output, it can be the state of an object etc. depends on your implementation.
Advantage of Java toString() method
By overriding the toString() method of the Object class, we can return values of the object, so we don't need to write much code.
Output without toString() method
class Student{
int id;
String name;
String address;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
}
public static void main(String args[]){
Student s1=new Student(100,”Joe”,”success”);
Student s2=new Student(50,”Jeff”,”fail”);
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Output:Student#2kaa9dc
Student#4bbc148
You can see in the above example #1. printing s1 and s2 prints the Hashcode values of the objects but I want to print the values of these objects. Since java compiler internally calls toString() method, overriding this method will return the specified values. Let's understand it with the example given below:
Example#2
Output with overriding toString() method
class Student{
int id;
String name;
String address;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
}
//overriding the toString() method
public String toString(){
return id+" "+name+" "+address;
}
public static void main(String args[]){
Student s1=new Student(100,”Joe”,”success”);
Student s2=new Student(50,”Jeff”,”fail”);
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Output:100 Joe success
50 Jeff fail
Note that toString() mostly is related to the concept of polymorphism in Java.
In, Eclipse, try to click on toString() and right click on it.Then, click on Open Declaration and see where the Superclass toString() comes from.
As others explained, the toString is not the place to be instantiating your class. Instead, the toString method is intended to build a string representing the value of an instance of your class, reporting on at least the most important fields of data stored in that object. In most cases, toString is used for debugging and logging, not for your business logic (except some historical methods, like Integer.toString()).
To generate text representing the value of an object for display to a user, add another method. People often name the method something like getDisplayName. For example, DayOfWeek::getDisplayName and Month::getDisplayName.
StringJoiner
As of Java 8 and later, the most modern way to implement toString would use the StringJoiner class. As the doc says:
StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
Use like this:
#Override
public String toString ()
{
return new StringJoiner( // In Java 8 and later, StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
" | " , // Delimiter
Person.class.getSimpleName() + "[ " , // Prefix
" ]" // Suffix
)
.add( "name=" + name ) // Append
.add( "phone=" + phone ) // Append
.toString(); // Convert entire sequence to a single `String` object.
}
Person[ name=Alice | phone=555.867.5309 ]
record
Java 16 brings a new way to briefly define a class where the main purpose is to communicate data transparently and immutably: record.
You define a record by merely listing the type and name of each member field. The compiler implicitly creates the constructor, getters, equals & hashCode, and toString.
Default implementation of toString
The default implementation of toString includes each and every member field.
public Kid ( String name , double height , LocalDate birthDate ) {}
Instantiate like any other object.
Kid alice = new Kid( "Alice" , 6.1d , LocalDate.of( 2019 , Month.April , 23 ) ) ;
String output = alice.toString() ;
You may choose to override the default implementation with your own. Overrides are usually not needed given the purpose of a record as a simple data-carrier.
You can creating new object in the toString().
use
return "Name = " + this.name +" height= " + this.height;
instead of
return Kid(this.name, this.height, this.bDay);
You may change the return string as required. There are other ways to store date instead calander.
You can't call a constructor as if it was a normal method, you can only call it with new to create a new object:
Kid newKid = new Kid(this.name, this.height, this.bDay);
But constructing a new object from your toString() method is not what you want to be doing.
Following code is a sample. Question based on the same, instead of using IDE based conversion, is there a faster way to implement so that in future the changes occur, we do not need to modify the values over and over again?
#Override
public String toString() {
return "ContractDTO{" +
"contractId='" + contractId + '\'' +
", contractTemplateId='" + contractTemplateId + '\'' +
'}';
}
If you're interested in Unit-Tests, then you can declare a public "ToStringTemplate", and then you can unit test your toString. Even if you don't unit-test it, I think its "cleaner" and uses String.format.
public class Kid {
public static final String ToStringTemplate = "KidName='%1s', Height='%2s', GregCalendar='%3s'";
private String kidName;
private double height;
private GregorianCalendar gregCalendar;
public String getKidName() {
return kidName;
}
public void setKidName(String kidName) {
this.kidName = kidName;
}
public double getHeight() {
return height;
}
public void setHeight(double height) {
this.height = height;
}
public GregorianCalendar getGregCalendar() {
return gregCalendar;
}
public void setGregCalendar(GregorianCalendar gregCalendar) {
this.gregCalendar = gregCalendar;
}
public String toString() {
return String.format(ToStringTemplate, this.getKidName(), this.getHeight(), this.getGregCalendar());
}
}
Now you can unit test by create the Kid, setting the properties, and doing your own string.format on the ToStringTemplate and comparing.
making ToStringTemplate static-final means "ONE VERSION" of the truth, rather than having a "copy" of the template in the unit-test.
The best way in my opinion is using google gson library:
#Override
public String toString() {
return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}
or apache commons lang reflection way
Well actually you will need to return something like this because toString has to return a string
public String toString() {
return "Name :" + this.name + "whatever :" + this.whatever + "";
}
and you actually do something wrong in the constructer you set the variable the user set to the name while you need to do the opposite.
What you shouldn't do
n = this.name
What you should do
this.name = n
Hopes this helps thanks
we can even write like this by creating a new String object in the class and assigning it what ever we want in constructor and return that in toString method which is overridden
public class Student{
int id;
String name;
String address;
String details;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
this.details=id+" "+name+" "+address;
}
//overriding the toString() method
public String toString(){
return details;
}
public static void main(String args[]){
Student s1=new Student(100,"Joe","success");
Student s2=new Student(50,"Jeff","fail");
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Nice and concise way is to use Lombok annotations. It has #ToString annotation, which will generate an implementation of the toString() method. By default, it will print your class name, along with each field, in order, separated by commas.
You can easily customize your output by passing parameters to annotation, e.g.:
#ToString(of = {"name", "lastName"})
Which is equivalent of pure Java:
public String toString() {
return "Person(name=" + this.name + ", lastName=" + this.experienceInYears + ")";
}
If you're just using toString() for debugging a DTO, you can generate human readable output automatically with something like the following:
import com.fasterxml.jackson.databind.ObjectMapper;
...
public String toString() {
try { return new ObjectMapper().writeValueAsString(this); }
catch (Exception e) { return "{ObjectMapper failed}"; }
}
However, this isn't appropriate for production deployments if the DTO may contain PII (which shouldn't be captured in logs).
Always have easy way: Right Click > Generate > toString() > select template that you want.
if you are use using notepad:
then
public String toString(){
return ""; ---now here you can use variables which you have created for your class
}
if you are using eclipse IDE then
press
-alt +shift +s
-click on override toString method here you will get options to select what type of variables you want to select.
But then in the toString() method you aren't actually returning a String, are you?
You'll have to return a String for this method to work.
public String toString() {
return "Name : " + this.name + " Height : " + this.height + " BirthDay : " + this.bday;
}
Sounds a little stupid, but I need help on my toString() method and it is very irking.
I tried looking up online because the toString is the one where it is screwing up and "not finding Kid constructor #2" even though it is there and I would even do something else and it doesn't work.
Ok that was a lot so here is my code:
import java.util.*;
class Kid {
String name;
double height;
GregorianCalendar bDay;
public Kid () {
this.name = "HEAD";
this.height = 1;
this.bDay = new GregorianCalendar(1111,1,1);
}
public Kid (String n, double h, String date) {
// method that toString() can't find somehow
StringTokenizer st = new StringTokenizer(date, "/", true);
n = this.name;
h = this.height;
}
public String toString() {
return Kid(this.name, this.height, this.bDay);
}
} //end class
Ok So my toString above (I know, my third parameter is off, should be a String) is off. If I hardcode a value in for the third thing it goes haywire and says it can't find this (up above). So how can I get the date and break it up?
Class calling this is below
class Driver {
public static void main (String[] args) {
Kid kid1 = new Kid("Lexie", 2.6, "11/5/2009");
System.out.println(kid1.toString());
} //end main method
} //end class
I tried researching multiple constructors and it really didn't help.
I tried researching toString() methods, and tried using previous toString() methods logic that I created previous but this is brand new so it never worked.
Help?
The toString is supposed to return a String.
public String toString() {
return "Name: '" + this.name + "', Height: '" + this.height + "', Birthday: '" + this.bDay + "'";
}
I suggest you make use of your IDE's features to generate the toString method. Don't hand-code it.
For instance, Eclipse can do so if you simply right-click on the source code and select Source > Generate toString
Java toString() method
If you want to represent any object as a string, toString() method comes into existence.
The toString() method returns the string representation of the object.
If you print any object, java compiler internally invokes the toString() method on the object. So overriding the toString() method, returns the desired output, it can be the state of an object etc. depends on your implementation.
Advantage of Java toString() method
By overriding the toString() method of the Object class, we can return values of the object, so we don't need to write much code.
Output without toString() method
class Student{
int id;
String name;
String address;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
}
public static void main(String args[]){
Student s1=new Student(100,”Joe”,”success”);
Student s2=new Student(50,”Jeff”,”fail”);
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Output:Student#2kaa9dc
Student#4bbc148
You can see in the above example #1. printing s1 and s2 prints the Hashcode values of the objects but I want to print the values of these objects. Since java compiler internally calls toString() method, overriding this method will return the specified values. Let's understand it with the example given below:
Example#2
Output with overriding toString() method
class Student{
int id;
String name;
String address;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
}
//overriding the toString() method
public String toString(){
return id+" "+name+" "+address;
}
public static void main(String args[]){
Student s1=new Student(100,”Joe”,”success”);
Student s2=new Student(50,”Jeff”,”fail”);
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Output:100 Joe success
50 Jeff fail
Note that toString() mostly is related to the concept of polymorphism in Java.
In, Eclipse, try to click on toString() and right click on it.Then, click on Open Declaration and see where the Superclass toString() comes from.
As others explained, the toString is not the place to be instantiating your class. Instead, the toString method is intended to build a string representing the value of an instance of your class, reporting on at least the most important fields of data stored in that object. In most cases, toString is used for debugging and logging, not for your business logic (except some historical methods, like Integer.toString()).
To generate text representing the value of an object for display to a user, add another method. People often name the method something like getDisplayName. For example, DayOfWeek::getDisplayName and Month::getDisplayName.
StringJoiner
As of Java 8 and later, the most modern way to implement toString would use the StringJoiner class. As the doc says:
StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
Use like this:
#Override
public String toString ()
{
return new StringJoiner( // In Java 8 and later, StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
" | " , // Delimiter
Person.class.getSimpleName() + "[ " , // Prefix
" ]" // Suffix
)
.add( "name=" + name ) // Append
.add( "phone=" + phone ) // Append
.toString(); // Convert entire sequence to a single `String` object.
}
Person[ name=Alice | phone=555.867.5309 ]
record
Java 16 brings a new way to briefly define a class where the main purpose is to communicate data transparently and immutably: record.
You define a record by merely listing the type and name of each member field. The compiler implicitly creates the constructor, getters, equals & hashCode, and toString.
Default implementation of toString
The default implementation of toString includes each and every member field.
public Kid ( String name , double height , LocalDate birthDate ) {}
Instantiate like any other object.
Kid alice = new Kid( "Alice" , 6.1d , LocalDate.of( 2019 , Month.April , 23 ) ) ;
String output = alice.toString() ;
You may choose to override the default implementation with your own. Overrides are usually not needed given the purpose of a record as a simple data-carrier.
You can creating new object in the toString().
use
return "Name = " + this.name +" height= " + this.height;
instead of
return Kid(this.name, this.height, this.bDay);
You may change the return string as required. There are other ways to store date instead calander.
You can't call a constructor as if it was a normal method, you can only call it with new to create a new object:
Kid newKid = new Kid(this.name, this.height, this.bDay);
But constructing a new object from your toString() method is not what you want to be doing.
Following code is a sample. Question based on the same, instead of using IDE based conversion, is there a faster way to implement so that in future the changes occur, we do not need to modify the values over and over again?
#Override
public String toString() {
return "ContractDTO{" +
"contractId='" + contractId + '\'' +
", contractTemplateId='" + contractTemplateId + '\'' +
'}';
}
If you're interested in Unit-Tests, then you can declare a public "ToStringTemplate", and then you can unit test your toString. Even if you don't unit-test it, I think its "cleaner" and uses String.format.
public class Kid {
public static final String ToStringTemplate = "KidName='%1s', Height='%2s', GregCalendar='%3s'";
private String kidName;
private double height;
private GregorianCalendar gregCalendar;
public String getKidName() {
return kidName;
}
public void setKidName(String kidName) {
this.kidName = kidName;
}
public double getHeight() {
return height;
}
public void setHeight(double height) {
this.height = height;
}
public GregorianCalendar getGregCalendar() {
return gregCalendar;
}
public void setGregCalendar(GregorianCalendar gregCalendar) {
this.gregCalendar = gregCalendar;
}
public String toString() {
return String.format(ToStringTemplate, this.getKidName(), this.getHeight(), this.getGregCalendar());
}
}
Now you can unit test by create the Kid, setting the properties, and doing your own string.format on the ToStringTemplate and comparing.
making ToStringTemplate static-final means "ONE VERSION" of the truth, rather than having a "copy" of the template in the unit-test.
The best way in my opinion is using google gson library:
#Override
public String toString() {
return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}
or apache commons lang reflection way
Well actually you will need to return something like this because toString has to return a string
public String toString() {
return "Name :" + this.name + "whatever :" + this.whatever + "";
}
and you actually do something wrong in the constructer you set the variable the user set to the name while you need to do the opposite.
What you shouldn't do
n = this.name
What you should do
this.name = n
Hopes this helps thanks
we can even write like this by creating a new String object in the class and assigning it what ever we want in constructor and return that in toString method which is overridden
public class Student{
int id;
String name;
String address;
String details;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
this.details=id+" "+name+" "+address;
}
//overriding the toString() method
public String toString(){
return details;
}
public static void main(String args[]){
Student s1=new Student(100,"Joe","success");
Student s2=new Student(50,"Jeff","fail");
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Nice and concise way is to use Lombok annotations. It has #ToString annotation, which will generate an implementation of the toString() method. By default, it will print your class name, along with each field, in order, separated by commas.
You can easily customize your output by passing parameters to annotation, e.g.:
#ToString(of = {"name", "lastName"})
Which is equivalent of pure Java:
public String toString() {
return "Person(name=" + this.name + ", lastName=" + this.experienceInYears + ")";
}
If you're just using toString() for debugging a DTO, you can generate human readable output automatically with something like the following:
import com.fasterxml.jackson.databind.ObjectMapper;
...
public String toString() {
try { return new ObjectMapper().writeValueAsString(this); }
catch (Exception e) { return "{ObjectMapper failed}"; }
}
However, this isn't appropriate for production deployments if the DTO may contain PII (which shouldn't be captured in logs).
Always have easy way: Right Click > Generate > toString() > select template that you want.
if you are use using notepad:
then
public String toString(){
return ""; ---now here you can use variables which you have created for your class
}
if you are using eclipse IDE then
press
-alt +shift +s
-click on override toString method here you will get options to select what type of variables you want to select.
But then in the toString() method you aren't actually returning a String, are you?
You'll have to return a String for this method to work.
public String toString() {
return "Name : " + this.name + " Height : " + this.height + " BirthDay : " + this.bday;
}
I was looking arround for this, but I couldn´t find a right answer.
I´m trying to get any field from an entity based on it´s column name.
Like a generic get, in which it receives a String columnName and returns an Object field that represents the Class field which is mapped by that columnName by Hibernate.
For example
#Table(name="ENTITY_EXAMPLE")
public class EntityExample{
#Column(name="COL_NAME")
private String name;
#Column(name="COL_SURNAME")
private String surname;
public EntityExample(String name, String surname){
this.name=name;
this.surname=surname;
}
//getters and setters
public Object getField(String columnName){
Object field=//some way to map the columnName with the field;
return field;
}
}
public main(String[] args){
EntityExample example=new EntityExample("John", "Doe");
String exampleName=(String) example.getField("COL_NAME");
String exampleSurname=(String) example.getField("COL_SURNAME");
System.out.println("NAME: "+ exampleName+ ", SURNAME: "+exampleSurname);
}
and that main when runs should print:
NAME: John, SURNAME: Doe
The way I´m doing now is with ifs that checks if the parameter is equal to each annotated column and inside returns the field if equals, but it should be a propper way to do that.
way I'm doing now:
public Object getField(String columnName){
if(columnName.equals("COL_NAME")){
return name;
}
if(columnName.equals("COL_SURNAME")){
return surname;
}
}
Thanks in advance.
As far as I know, the way you're doing it, is the only way. With the exception being, to use a switch statement instead of multiple if statements:
switch (columnName) {
case 1: columnName = "COL_NAME";
return this.name;
break;
case 2: columnName= "COL_SURNAME";
return this.surname;
break;
default: columnName= "COL_BLAHBLAH";
return this.blahblhblah;
break;
}
The only possible way to what you want (and this is a big stretch), is if you did something along the lines of:
public Object getField(String columnName){
Object field= (Object)columnName;
return field;
}
Note: You would need to pass in the object name (aka: name,surname) and not the column name.
But I honestly don't think this is going to work. Regardless, you would need to cast a string as an object in such a way that the compiler would know how to handle the casting properly (don't think it's possible).
Good luck either way. Maybe someone else will have more ideas.
You can , of course, use reflection to go through the fields of your entity, looking for which one has the #Column annotation with the corresponding name. However, many people will tell you that Reflection is slow.
What we did to accomplish this was to create a set of public static integer constants for each of the columns. Thus in your entity you would have the following:
public static final int COL_NAME = 1;
public static final int COL_SURNAME = 2;
and in the Entity you also have a getFieldValue method as follows:
public Object getFieldValue(int fieldNo) {
switch (fieldNo) {
case COL_NAME:
return this.name;
case COL_SURNAME:
return this.surname;
default:
throw IllegalArgumentException("Invalid Field Number: " + fieldNo);
}
}
and you would use these to get fields values as follows:
String name = entityExample.getFieldValue(EntityExample.COL_NAME);
Of course, the problem you have now is maintaining both the list of constants and the switch cases when columns are added/removed/renamed. We get round this by using a script to generate both the constants and the method. You could also use Java's annotation processing to generate the same code.
Is there any way in which I can automatically convert a Custom Class Object into a human readable string?
e.g. consider the following class:
class Person {
String Name;
int Salary;
...
}
Person p = new Person();
p.setName("Tony");
p.setSalary(1000);
I need to get something like:
Person: Name="Tony", Salary=1000
Importing Commons Lang you could use ToStringBuilder
Check method reflectionToString(java.lang.Object), this will create automatically the representation you are expecting.
This code:
Person p = new Person();
p.setName("Tony");
p.setSalary(1000);
System.out.println(ToStringBuilder.reflectionToString(p));
results this string:
Person#64578ceb[Name=Tony,Salary=1000]
sure you can override the toString method of class.
as follow:
class Person {
String name;
int salary;
...
#Override public String toString() {
return "Person: Name='" + name + "', Salary=" + salary;
}
}
refer for more details https://blogs.oracle.com/CoreJavaTechTips/entry/writing_tostring_methods_tech_days
This is basically what toString is for. But given you want this done automatically, you can create some general service that can do it. Use reflection to iterate all fields, and then print each one's name and value. Simplest way to print their values would be by using their toString, but you can also pass them into that printing service recursively on some cases (you'll have to find the halt condition, of course).
For example, on some class PrintUtils have:
public static void printFields(Object o) {
System.out.print(o.getClass.getSimpleName() + ": ");
for (Field field : o.getClass().getDeclaredFields()) {
field.setAccessible(true); // you also get non-public fields
System.out.print(field.getName() + " = " + field.get(o) + ", ");
}
}
You'll have to handle exceptions etc. and possibly better format the output, of course. Also, this only print fields declared in the current class. If you want fields declared higher in the inheritance hierarchy, you'll have to work a bit more. Lastly, using reflection is much slower than just having a regular toString. If using toString is possible, it is preferable.
I think you could use ToStringBuilder that is part of commons-lang.
One way to do it is to rely on Apache Commons BeanUtils.describe. This will produce a Map of bean's properties, which converts to a string nicely via Map.toString. If you want something more custom, you'll need to dig into the reflection API.
You can use message format from java :
https://docs.oracle.com/javase/tutorial/i18n//message.html
seperate variable by - and there you have a humanreadable string of your class!
class Person {
String Name;
int Salary;
...
#Override
public String toString() {
return "Person: Name = " + Name + "," +
"Salary="+Salary;
}
}
Person p = new Person();
p.setName("Tony");
p.setSalary(1000);
System.out.println(p.toString());
Sounds a little stupid, but I need help on my toString() method and it is very irking.
I tried looking up online because the toString is the one where it is screwing up and "not finding Kid constructor #2" even though it is there and I would even do something else and it doesn't work.
Ok that was a lot so here is my code:
import java.util.*;
class Kid {
String name;
double height;
GregorianCalendar bDay;
public Kid () {
this.name = "HEAD";
this.height = 1;
this.bDay = new GregorianCalendar(1111,1,1);
}
public Kid (String n, double h, String date) {
// method that toString() can't find somehow
StringTokenizer st = new StringTokenizer(date, "/", true);
n = this.name;
h = this.height;
}
public String toString() {
return Kid(this.name, this.height, this.bDay);
}
} //end class
Ok So my toString above (I know, my third parameter is off, should be a String) is off. If I hardcode a value in for the third thing it goes haywire and says it can't find this (up above). So how can I get the date and break it up?
Class calling this is below
class Driver {
public static void main (String[] args) {
Kid kid1 = new Kid("Lexie", 2.6, "11/5/2009");
System.out.println(kid1.toString());
} //end main method
} //end class
I tried researching multiple constructors and it really didn't help.
I tried researching toString() methods, and tried using previous toString() methods logic that I created previous but this is brand new so it never worked.
Help?
The toString is supposed to return a String.
public String toString() {
return "Name: '" + this.name + "', Height: '" + this.height + "', Birthday: '" + this.bDay + "'";
}
I suggest you make use of your IDE's features to generate the toString method. Don't hand-code it.
For instance, Eclipse can do so if you simply right-click on the source code and select Source > Generate toString
Java toString() method
If you want to represent any object as a string, toString() method comes into existence.
The toString() method returns the string representation of the object.
If you print any object, java compiler internally invokes the toString() method on the object. So overriding the toString() method, returns the desired output, it can be the state of an object etc. depends on your implementation.
Advantage of Java toString() method
By overriding the toString() method of the Object class, we can return values of the object, so we don't need to write much code.
Output without toString() method
class Student{
int id;
String name;
String address;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
}
public static void main(String args[]){
Student s1=new Student(100,”Joe”,”success”);
Student s2=new Student(50,”Jeff”,”fail”);
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Output:Student#2kaa9dc
Student#4bbc148
You can see in the above example #1. printing s1 and s2 prints the Hashcode values of the objects but I want to print the values of these objects. Since java compiler internally calls toString() method, overriding this method will return the specified values. Let's understand it with the example given below:
Example#2
Output with overriding toString() method
class Student{
int id;
String name;
String address;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
}
//overriding the toString() method
public String toString(){
return id+" "+name+" "+address;
}
public static void main(String args[]){
Student s1=new Student(100,”Joe”,”success”);
Student s2=new Student(50,”Jeff”,”fail”);
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Output:100 Joe success
50 Jeff fail
Note that toString() mostly is related to the concept of polymorphism in Java.
In, Eclipse, try to click on toString() and right click on it.Then, click on Open Declaration and see where the Superclass toString() comes from.
As others explained, the toString is not the place to be instantiating your class. Instead, the toString method is intended to build a string representing the value of an instance of your class, reporting on at least the most important fields of data stored in that object. In most cases, toString is used for debugging and logging, not for your business logic (except some historical methods, like Integer.toString()).
To generate text representing the value of an object for display to a user, add another method. People often name the method something like getDisplayName. For example, DayOfWeek::getDisplayName and Month::getDisplayName.
StringJoiner
As of Java 8 and later, the most modern way to implement toString would use the StringJoiner class. As the doc says:
StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
Use like this:
#Override
public String toString ()
{
return new StringJoiner( // In Java 8 and later, StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
" | " , // Delimiter
Person.class.getSimpleName() + "[ " , // Prefix
" ]" // Suffix
)
.add( "name=" + name ) // Append
.add( "phone=" + phone ) // Append
.toString(); // Convert entire sequence to a single `String` object.
}
Person[ name=Alice | phone=555.867.5309 ]
record
Java 16 brings a new way to briefly define a class where the main purpose is to communicate data transparently and immutably: record.
You define a record by merely listing the type and name of each member field. The compiler implicitly creates the constructor, getters, equals & hashCode, and toString.
Default implementation of toString
The default implementation of toString includes each and every member field.
public Kid ( String name , double height , LocalDate birthDate ) {}
Instantiate like any other object.
Kid alice = new Kid( "Alice" , 6.1d , LocalDate.of( 2019 , Month.April , 23 ) ) ;
String output = alice.toString() ;
You may choose to override the default implementation with your own. Overrides are usually not needed given the purpose of a record as a simple data-carrier.
You can creating new object in the toString().
use
return "Name = " + this.name +" height= " + this.height;
instead of
return Kid(this.name, this.height, this.bDay);
You may change the return string as required. There are other ways to store date instead calander.
You can't call a constructor as if it was a normal method, you can only call it with new to create a new object:
Kid newKid = new Kid(this.name, this.height, this.bDay);
But constructing a new object from your toString() method is not what you want to be doing.
Following code is a sample. Question based on the same, instead of using IDE based conversion, is there a faster way to implement so that in future the changes occur, we do not need to modify the values over and over again?
#Override
public String toString() {
return "ContractDTO{" +
"contractId='" + contractId + '\'' +
", contractTemplateId='" + contractTemplateId + '\'' +
'}';
}
If you're interested in Unit-Tests, then you can declare a public "ToStringTemplate", and then you can unit test your toString. Even if you don't unit-test it, I think its "cleaner" and uses String.format.
public class Kid {
public static final String ToStringTemplate = "KidName='%1s', Height='%2s', GregCalendar='%3s'";
private String kidName;
private double height;
private GregorianCalendar gregCalendar;
public String getKidName() {
return kidName;
}
public void setKidName(String kidName) {
this.kidName = kidName;
}
public double getHeight() {
return height;
}
public void setHeight(double height) {
this.height = height;
}
public GregorianCalendar getGregCalendar() {
return gregCalendar;
}
public void setGregCalendar(GregorianCalendar gregCalendar) {
this.gregCalendar = gregCalendar;
}
public String toString() {
return String.format(ToStringTemplate, this.getKidName(), this.getHeight(), this.getGregCalendar());
}
}
Now you can unit test by create the Kid, setting the properties, and doing your own string.format on the ToStringTemplate and comparing.
making ToStringTemplate static-final means "ONE VERSION" of the truth, rather than having a "copy" of the template in the unit-test.
The best way in my opinion is using google gson library:
#Override
public String toString() {
return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}
or apache commons lang reflection way
Well actually you will need to return something like this because toString has to return a string
public String toString() {
return "Name :" + this.name + "whatever :" + this.whatever + "";
}
and you actually do something wrong in the constructer you set the variable the user set to the name while you need to do the opposite.
What you shouldn't do
n = this.name
What you should do
this.name = n
Hopes this helps thanks
we can even write like this by creating a new String object in the class and assigning it what ever we want in constructor and return that in toString method which is overridden
public class Student{
int id;
String name;
String address;
String details;
Student(int id, String name, String address){
this.id=id;
this.name=name;
this.address=address;
this.details=id+" "+name+" "+address;
}
//overriding the toString() method
public String toString(){
return details;
}
public static void main(String args[]){
Student s1=new Student(100,"Joe","success");
Student s2=new Student(50,"Jeff","fail");
System.out.println(s1);//compiler writes here s1.toString()
System.out.println(s2);//compiler writes here s2.toString()
}
}
Nice and concise way is to use Lombok annotations. It has #ToString annotation, which will generate an implementation of the toString() method. By default, it will print your class name, along with each field, in order, separated by commas.
You can easily customize your output by passing parameters to annotation, e.g.:
#ToString(of = {"name", "lastName"})
Which is equivalent of pure Java:
public String toString() {
return "Person(name=" + this.name + ", lastName=" + this.experienceInYears + ")";
}
If you're just using toString() for debugging a DTO, you can generate human readable output automatically with something like the following:
import com.fasterxml.jackson.databind.ObjectMapper;
...
public String toString() {
try { return new ObjectMapper().writeValueAsString(this); }
catch (Exception e) { return "{ObjectMapper failed}"; }
}
However, this isn't appropriate for production deployments if the DTO may contain PII (which shouldn't be captured in logs).
Always have easy way: Right Click > Generate > toString() > select template that you want.
if you are use using notepad:
then
public String toString(){
return ""; ---now here you can use variables which you have created for your class
}
if you are using eclipse IDE then
press
-alt +shift +s
-click on override toString method here you will get options to select what type of variables you want to select.
But then in the toString() method you aren't actually returning a String, are you?
You'll have to return a String for this method to work.
public String toString() {
return "Name : " + this.name + " Height : " + this.height + " BirthDay : " + this.bday;
}