Actually i am implementing one program in which i am retrieving information from database and i am setting that info to One Object using setters and i just want to print that Object parameters without using system.out.println(object.getHeadCount());
I just want like if i am giving system.out.println(object); so using this code it should print data in Json format or any other readable format.
How to do it.Because my object is containing 30 fields so it is very hectic to write 30 getters to print data.
You have to override toString()
Normal way
class User {
private String firstName;
private String lastName;
public User(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
#Override
public String toString(){
return this.firstName + " " + this.lastName;
}
}
Using Apache Commons
class User {
private String firstName;
private String lastName;
public User(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
#Override
public String toString(){
return new ToStringBuilder(this)
.append("firstName", firstName)
.append("lastName", lastName)
.toString();
}
}
Using Google Guava
class User {
private String firstName;
private String lastName;
public User(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
#Override
public String toString(){
return MoreObjects.toStringHelper(this)
.add("firstName", firstName)
.add("lastName", lastName)
.toString();
}
}
You simply have to override the toString() method of the class, read about it in java doc for Object class. Most IDE support it's automatic generation for all the fields of your class or for a number of them. Just for example:
class User {
private String name;
private String surname;
User(String name, String surname)
{
this.name = name;
this.surname = surname;
}
#Override
public String toString()
{
return this.name+" "+this.surname;
}
}
You should override toString() method. if you are using eclipse then you can try right-click within the editor, you'll find it under Source -> Generate toString()
To make a toString method you can simply just add one like so.
public String toString(){
return "" + getValue();
}
The toString method is a part of
java.lang.Object
So it is implemented in every class.
Related
I have a users database in firebase that contains user's first name and last name
So, i want to take only the head name (i.e) Stephen, Steve, Tony e.t.c.
And i want to show them as a list in a recycler view.
Is this possible?
This is my java object
public class Users {
String firstName, lastName;
public Users(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
and i have created my adapter that extends RecyclerView.Adapter<>
PS: The names are not always same as the first name.
I created a Lambda based on this URL: https://docs.aws.amazon.com/lambda/latest/dg/java-handler-io-type-pojo.html. There are three main classes:
package example;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
public class HelloPojo implements RequestHandler<RequestClass, ResponseClass>{
public ResponseClass handleRequest(RequestClass request, Context context){
String greetingString = String.format("Hello %s, %s.", request.firstName, request.lastName);
return new ResponseClass(greetingString);
}
}
is the Lambda handler.
package example;
public class RequestClass {
String firstName;
String lastName;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public RequestClass(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
public RequestClass() {
}
}
is the requestClass.
package example;
public class ResponseClass {
String greetings;
public String getGreetings() {
return greetings;
}
public void setGreetings(String greetings) {
this.greetings = greetings;
}
public ResponseClass(String greetings) {
this.greetings = greetings;
}
public ResponseClass() {
}
}
is the response class.
Input is something along the lines of:
{ "firstName": "John", "lastName": "Doe" }
That being said, I do have some questions regarding the RequestClass. Right now, it is dependent on there being a firstName and lastName provided as part of the input. However, let's say only a firstName is provided, and I want to have another constructor in the RequestClass with just a firstName parameter and initialize the lastName to a default lastName, something like
public RequestClass(String firstName) {
this.firstName = firstName;
this.lastName = "defaultLastName";
}
When I try doing something along these lines and access the variables in the handleRequest, I'm able to get the firstName but lastName is always null (guessing because I do not provide it as part of the input). Any reason as to why this happens and what I can do so that when accessing lastName in the handler class, I am able to get "defaultLastName" instead of null?
Please let me know if there are further clarifications I should add, I don't post to StackOverflow very often and want to make sure my question is appropriate!
you could set some default values in your default constructor.
public RequestClass() {
firstName = "defaultFirstName";
lastName = "defaultLastName;
}
And then call your parameterized constructor with this.
public RequestClass(String firstName) {
this();
this.firstName = firstName;
}
Readings for constructor overloading:
https://beginnersbook.com/2013/05/constructor-overloading/
I've built a Java application for, globally, mange computers database at my job. At first, I've been told that we needed a tab called 'Users', which would contain first name, last name and email. But now, the technician wants to add other fields such as address, phone, etc. He asked me if he could add himself these fields. The problem is, he's not a programmer. He wants to add these fields with a GUI. I have built the application with static fields, and here is my User Class.
public class User {
private String firstname;
private String lastname;
private String email;
private int id;
public User(String firstname, String lastname) {
this.firstname = firstname;
this.lastname = lastname;
}
public User(int id, String firstname, String lastname, String email) {
this.id = id;
this.firstname = firstname;
this.lastname = lastname;
this.email = email;
}
public User(String firstname, String lastname, String email) {
this.firstname = firstname;
this.lastname = lastname;
this.email = email;
}
public String getFirstname() {
return firstname;
}
public void setFirstname(String firstname) {
this.firstname = firstname;
}
public String getLastname() {
return lastname;
}
public void setLastname(String lastname) {
this.lastname = lastname;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public int getId() {
return id;
}
public String toString() {
return firstname + " " + lastname;
}
}
Now, I wonder if there's a way to modify this class using the GUI or if I have to rebuild entirely the software and stop using object classes like that. There are also classes like "Software" and "Operating Systems" that have static fields but need to be modified if necessary.
I don't know what options exactly I have to get the job done:
Let the tech modify the database and do something like "for each column in database, add this column in the GUI". (Which would cause to rebuild the entire software.)
others?
Any reads/tutorials on that kind of issues?
Thanks.
If the requirement is that a normal user should be able to add additonal fields to existing objects, propably the best way would be to store the information in a map.
So instead of:
public class User {
private String firstname;
private String lastname;
private String email;
private int id;
}
you would have:
public class User {
private int id;
private Map<String,String> properties;
public User(String firstname, String lastname) {
properties = new HashMap<String,String>();
properties.put("firstname",firstname);
properties.put("lastname",lastname);
}
etc.
Good day,
I am new to JAVA'm learning this language and what I have learned it seems a fantastic language. My question is in relation to the following:
Suppose I have a class like this:
public class Person{
private String firstName;
private String lastName;
private int age;
private String entireName;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getEntireName() {
return entireName;
}
public void setEntireName(String entireName) {
this.entireName = entireName;
}
public static void Main(String args[]){
Person person = new Person();
person.setFirstName("Jhon");
person.setLastName("Adams");
person.setAge(20);
//Atention this line
person.setEntireName(person.getFirstName()+person.getLastName());
}
}
The language allows me to do this: person.setEntireName(person.getFirstName()+person.getLastName());
and it works fine however I would like to know how is best to do this, how it behaves at the object level and how high or low the performance.
Thank you ..
What you do is perfectly valid, but not very logical. Why not just drop the setEntireName() since it just combines two existing fields?
public String getEntireName() {
return firstName + " " + lastname;
}
This is valid. There is no performance difference, becasue JIT compiler optimize this code if needed (simply replace method with fields access).
Typically it is easier to eliminate the entireName property and its setter, and use the getter to perform the concatenation like so:
public String getEntireName() {
return firstName + " " + lastName;
}
This is also easier to maintain than updating entireName every time firstName or lastName is changed.
New to Java...
I have a name class that has:
private String firstName;
private String middleInitial;
private String lastName;
as its instance variables.
If I had certain data that had only firstName and lastName, no middleInitial, how would I make the constructor so that it took only 2 parameters instead of three?
You simply write a constructor with two parameters and a constructor with three
public YourClass(String firstName, String lastName) {
...
}
public YourClass(String firstName, String middleInitial, String lastName) {
...
}
Callers can then choose to use the appropriate constructor based on their needs.
Well, two options:
Just have a constructor with three parameters, and call it using null or the empty string for middleInitial
Overload the constructors, possibly calling one from the other.
As an example for the latter, using an empty string as the default middle initial:
public Person(String firstName, String middleInitial, String lastName)
{
this.firstName = firstName;
this.middleInitial = middleInitial;
this.lastName = lastName;
}
public Person(String firstName, String lastName)
{
this(firstName, "", lastName);
}
However, the compiler will need to know which one you're calling from the call site. So you can do:
new Person("Jon", "L", "Skeet");
or
new Person("Jon", "Skeet");
... but you can't do:
// Invalid
new Person(firstName, gotMiddleInitial ? middleInitial : ???, lastName);
and expect the compiler to decide to use the "two name" variant instead.
In Java, constructors can't have default arguments. Your only option here is to write two constructors. Fortunately, Java does allow you to call constructors from other constructors. You could do something like:
public class MyClass {
private String firstName;
private String middleInitial;
private String lastName;
public MyClass(String firstName, String middleInitial, String lastName) {
this.firstName = firstName;
this.middleInitial = middleInitial;
this.lastName = lastName;
}
public MyClass(String firstName, String lastName) {
this(firstName, "", lastName);
}
...
}
public Class Name{
private String first;
private String middle;
private String last;
public Name(String first, String middle, String last){
this.first = first;
this.middle = middle;
this.last = last;
}
public Name(String first, String last){
this.first = first;
this.last = last;
}
}
You could use two constructors:
public Person(String firstName, String lastName)
{
this(firstName, null, lastName);
}
public Person(String firstName, String middleInitial, String lastName)
{
this.firstName = firstName;
this.middleInitial = middleInitial;
this.lastName = = lastName;
}
Define 2 constructors, one with 2 parameters and one with 3 parameters.
You can write two constructors.
public Person( String firstName, String lastName, String middleName ) { ... }
public Person( String firstName, String lastName ) { ... }
public void myBike(String name, String color)
{
System.out.println("My bike's name is " + name + " and is " + color + ".");
}
public void myBike(String name, String color, float height)
{
System.out.println("My bike's name is " + name + " and is " + color + ".");
System.out.println("My bike is also " + height + " inches tall.");
}
Builder pattern...
class Name {
Builder builder;
public String getSurname() {
return builder.surname;
}
// getter...
public Name(Builder builder) {
this.builder = builder;
}
class Builder {
String surname = "";
String middleName = "";
String name = "";
Builder surname(String surname) {
this.surname = surname;
return this;
}
Builder middleName(String middleName) {
this.middleName = middleName;
return this;
}
Builder name(String name) {
this.name = name;
return this;
}
Name build() {
return new Name(this);
}
}
}