Develop Reference

How do you update/change a instance variable in Java? (Beginner Level)

I am new to java, and I am trying to create a method to update the instance variable age for my objects. I am getting the code to compile, but I am seeing no change in the age value. This code is part of an assignment, so I cannot change the constructors. The method I wrote to update the age (that doesn't work) is shown below. My entire code is shown below that. I am also curious if there's a way to update/change just one of my objects, but before I do that, I need the method to work for both. Any help writing this method properly would be appreciated!
public void setnewAge(int age) {
dogAge += 1;
this.dogAge = dogAge;
}
Below is my entire code (including the method I wrote to update age).
public class Dog {
//Instance Varibles
private String dogName;
private int dogAge;
private int dogWeight;
//Two Contructors (One Completely Empty)
public Dog() {
}
public Dog(String name, int age, int weight){
dogName = name;
dogAge = age;
dogWeight = weight;
}
//Getters
public String getName() { return dogName;}
public int getAge() { return dogAge;}
public int getWeight() { return dogWeight;}
//Setters
public void setName(String theName) { dogName = theName;}
public void setAge(int theAge) {dogAge = theAge;}
public void setWeight(int theWeight) {dogWeight = theWeight;}
//to(String) method
public String toString() {
return "The dogs's name is " + getName() + ", the dogs's age is " +
getAge() + ", " + "\n" + "the dogs's weight is " + getWeight() + ".";
}
public void setnewAge(int age) {
dogAge += 1;
this.dogAge = dogAge;
}
//Main Method
public static void main(String[] args) {
Dog poodle = new Dog("Bob", 5, 26);
System.out.println(poodle);
Dog lab = new Dog();
lab.setName("Steve");
lab.setAge(8);
lab.setWeight(43);
System.out.println(lab);
}
}

As Tom said, you need to actually call the function in your main function otherwise, there will be no change, and also to refine your code for your setnewAge function, try this:
public void setnewAge() {
this.dogAge = dogAge + 1;
}
Then in the main function call setnewAge() and then print your age to see the results.
Dog poodle = new Dog("Bob", 5, 26);
poodle.setnewAge() ;

Creating a method and returning object

I am extremely stuck on this assignment I have, this is the last part of the assignment and it is going over my head. We were given this code to start off with.
import java.util.*;
import java.io.*;
public class TestEmployee2
{
public static void main(String[] args) throws IOException
{
Employee e1 = new Employee2(7, "George Costanza");
e1.setDepartment("Front Office");
e1.setPosition("Assistant to the Traveling Secretary");
e1.setSalary(50000.0);
e1.setRank(2);
e1.displayEmployee();
//Employee e2 = createEmployeeFromFile();
//e2.displayEmployee();
}
}
We were told to create a method called createEmployeeFromFile();. In this method we are to read from a .txt file with a Scanner and use the data to create an Employee object. Now I am confused on two things. First on the method type I should be using, and how to create an object with the data from the .txt file. This is the first time we have done this and it is difficult for me. Employee1 works fine, but when trying to create my method I get stuck on what to create it as.
Here is my rough draft code for right now.
import java.util.*;
import java.io.*;
public class TestEmployee2
{
public static void main(String[] args) throws IOException
{
EckEmployee2 e1 = new EckEmployee2(7, "George Costanza");
EckEmployee2 e2 = createEmployeeFromFile();
e1.setDepartment("Front Office");
e1.setPosition("Assistant to the Traveling Secretary");
e1.setSalary(50000.0);
e1.setRank(2);
e2.setNumber();
e2.setName();
e2.setDepartment();
e2.setPosition();
e2.setSalary();
e2.setRank();
e1.displayEmployee();
e2.displayEmployee();
}
createEmployeeFromFile(){
File myFile = new File("employee1.txt");
Scanner kb = new Scanner(myFile);
}
}
I am not expecting to get the answer just someone to point me in the right direction. Any help is greatly appreciated.
Here is my code from my main class.
public class EckEmployee2 {
private int rank;
private double number;
private double salary;
private String name;
private String department;
private String position;
public EckEmployee2() {
number = 0;
name = null;
department = null;
position = null;
salary = 0;
rank = 0;
}
public EckEmployee2(double number, String name) {
this.number = number;
this.name = name;
}
public EckEmployee2(double number, String name, String department, String position, double salary, int rank) {
this.number = number;
this.name = name;
this.department = department;
this.position = position;
this.salary = salary;
this.rank = rank;
}
public void setNumber(double num) {
this.number = num;
}
public double getNumber() {
return this.number;
}
public void setName(String nam) {
this.name = nam;
}
public String getName() {
return this.name;
}
public void setDepartment(String dept) {
this.department = dept;
}
public String getDepartment() {
return this.department;
}
public void setPosition(String pos) {
this.position = pos;
}
public String getPosition() {
return this.position;
}
public void setSalary(double sal) {
this.salary = sal;
}
public double getSalary() {
return this.salary;
}
public void setRank(int ran) {
this.rank = ran;
}
public int getRank() {
return this.rank;
}
public boolean checkBonus() {
boolean bonus = false;
if (rank < 5) {
bonus = false;
} else if (rank >= 5)
bonus = true;
return bonus;
}
public void displayEmployee() {
if (checkBonus() == true) {
System.out.println("-------------------------- ");
System.out.println("Name: " + name);
System.out.printf("Employee Number: %09.0f\n" , number, "\n");
System.out.println("Department: \n" + department);
System.out.println("Position: \n" + position);
System.out.printf("Salary: %,.2\n" , salary);
System.out.println("Rank: \n" + rank);
System.out.printf("Bonus: $\n", 1000);
System.out.println("-------------------------- ");
} else if (checkBonus() == false)
System.out.println("--------------------------");
System.out.println("Name: " + name);
System.out.printf("Employee Number: %09.0f\n" , number, "\n");
System.out.println("Department: " + department);
System.out.println("Position: " + position);
System.out.printf("Salary: %,.2f\n" , salary);
System.out.println("Rank: " + rank);
System.out.println("-------------------------- ");
}
}
To make things more clear here are the directions
Create a method in TestEmployee2 called createEmployeeFromFile() that will read data from a file and create, populate and return an Employee object. The file it will read from is called employee1.txt, which is provided. Hard code the name of the file in the method. This file contains the employee’s number, name, department, position, salary and rank. Create a Scanner object and use the Scanner class’s methods to read the data in the file and use this data to create the Employee object. Finally return the employee object.

In java, to return a value from a method, you add that objects type into the method signature as below, and in short java method signatures are as follows
'modifier (public, private, protected)' 'return type (void/nothing, int, long, Object, etc...' 'methodName(name the method)' 'parameters (any object or primitive as a parameter'
The method below will work if you have an employee contstructor which parses the input text, and assuming the data is split my a delimiter, you can use String.split(splitString); where splitString is the character that splits the data, i.e) a comma ",".
public EckEmployee2 getEmployee()
{
try
{
/**
* This will print where your java working directory is, when you run the file
*
*/
System.out.println(System.getProperty("user.dir"));
/**
* Gets the file
*/
File myFile = new File("employee1.txt");
/**
* Makes the scanner
*/
Scanner kb = new Scanner(myFile);
/**
* A list to store the data of the file into
*/
List<String> lines = new ArrayList<>();
/**
* Adds all the lines in the file to the list "lines"
*/
while (kb.hasNext())
{
lines.add(kb.next());
}
/**
* Now that you have the data from the file, assuming its one line here, you can parse the data to make
* your "Employee"
*/
if (lines.size() > 0)
{
final String line = lines.get(0);
return new EckEmployee2(line);
}
}
/**
* This is thrown if the file you are looking for is not found, it either doesn't exist or you are searching
* in the wrong directory.
*/
catch (FileNotFoundException e)
{
e.printStackTrace();
}
/**
* Return null if an exception is thrown or the file is empty
*/
return null;
}

First your method createEmployeeFromFile() must take 2 parameters, a Scanner object to read input, and the File you're gonna be reading from using the Scanner.
The return type is Empolyee2 because the method creates a Employee2 instance and must return it.
Now, I gave you the initiatives.
Your turn to read more about Scanner object and File object.
Reading from the text file, the attributes of your object, is easy then you create an instance by using the constructor with the attributes and return it!
Hope this helps.

Java inheritance - subclass method override

I am struggling with an inheritance task in Java
I was given an Animal.java class. My homework is to create a subclass called Lion.java. One of the tasks I'm struggling with within the entire task is outputting the type of Lion it is based on the weight of the lion. This is the code for the Animal.java
public class Animal {
private int numTeeth = 0;
private boolean spots = false;
private int weight = 0;
public Animal(int numTeeth, boolean spots, int weight){
this.setNumTeeth(numTeeth);
this.setSpots(spots);
this.setWeight(weight);
}
public int getNumTeeth(){
return numTeeth;
}
public void setNumTeeth(int numTeeth) {
this.numTeeth = numTeeth;
}
public boolean getSpots() {
return spots;
}
public void setSpots(boolean spots) {
this.spots = spots;
}
public int getWeight() {
return weight;
}
public void setWeight(int weight) {
this.weight = weight;
}
public static void main(String[] args){
Lion lion = new Lion(30, false, 80);
System.out.println(lion);
}
}
This is my code for the Lion.java class so far:
public class Lion extends Animal {
String type = "";
public Lion(int numTeeth, boolean spots, int weight) {
super(numTeeth, spots, weight);
}
public String type(int weight){
super.setWeight(weight);
if(weight <= 80){
type = "Cub";
}
else if(weight <= 120){
type = "Female";
}
else{
type = "Male";
}
return type;
}
#Override
public String toString() {
String output = "Number of Teeth: " + getNumTeeth();
output += "\nDoes it have spots?: " + getSpots();
output += "\nHow much does it weigh: " + getWeight();
output += "\nType of Lion: " + type;
return output;
The problem is the output does not return the type based on the if statement above. It's probably a very simple solution but I can't seem to figure it out.

In toString method, instead of type replace with type() method.
#Override
public String toString() {
String output = "Number of Teeth: " + getNumTeeth();
output += "\nDoes it have spots?: " + getSpots();
output += "\nHow much does it weigh: " + getWeight();
output += "\nType of Lion: " + type(getWeight());
return output;

Take a good look at your Lion constructor
public Lion(int numTeeth, boolean spots, int weight) {
super(numTeeth, spots, weight);
}
This doesn't do anything for the type (your public type method).
In order to set the private type class variable you need to either call the type method in the constructor or after the object has been created but before you call the toString method. For example
public Lion(int numTeeth, boolean spots, int weight) {
super(numTeeth, spots, weight);
type(weight);
}
Note that, as pointed out in the comments, you probably would be better off handling the type directly in the setWeight method. You can do something like
#Override
public void setWeight(int weight) {
super.setWeight(weight);
type(weight);
}
and leave the constructor alone.
Taking it one step further, you could refactor your code such that the type method has no parameter (you've already set the weight member).

Print the value of a Java constructor

I am a java beginner and I am trying to get used to objects. Is there anyway that I can print out the value of a constructor in main? How can I print out the value's Kevin,20? Thanks
public class MainConstructor {
public static void main(String[] args) {
ConstructorClass emp1 = new ConstructorClass("Kevin", 20);
}
}
//Constructor Class
public class ConstructorClass {
private String name;
private int number;
public ConstructorClass(String name, int number) {
this.name = name;
this.number = number;
System.out.println("called");
}
}

Add a toString() method to ConstructorClass:
public String toString() {
return name + "," + number;
}
Then call this from main:
public static void main(String[] args) {
ConstructorClass emp1 = new ConstructorClass("Kevin",20);
System.out.println(emp1.toString());
}

Try using toString() in your class
public String toString() {
return this.name + "," + this.number;
}
and in your main just do emp1.toString(); to print it to your console

Constructor is basically just another method (but for the love of what is holy, never say that during interview or even to your professor) so there is nothing wrong with doing this:
public class ConstructorClass {
private String name;
private int number;
public ConstructorClass(String name, int number) {
this.name = name;
this.number = number;
System.out.println(name+" "+number);
}
}
But this solution is really ugly and kind of "hotfixy". Better solution would be to have constructor to only get the values and have separate method to print what you want:
public ConstructorClass(String name, int number) {
this.name = name;
this.number = number;
}
void printNameAndNumber() {
System.out.println(name+" "+number);
}
And use the class like this in your main
ConstructorClass c = new ConstructorClass("John",85)
c.printNameAndNumber();
Also some people like to handle this by going through hoops and loops and overriding ToString, but that is being too overzealous and there is really no benefit in your case (or any other primitive case).

public ConstructorClass(String name, int number) {
this.name = name;
this.number = number;
System.out.println(name + "," + number);
}

If you want to properly print out those values, you should have getter methods set in your methods
Example below
public String getName(){
return name;
}
public int getNumber(){
return number;
}
Then to print those values, you should then use methods toString() and method print() to display your values
Example
public String toString(){
return getName() + " " + getNumber();
}
public void print(){
System.out.println(toString());
}
Then in the class with the main method, you call your print method for that specific class
Example
ConstructorClass emp1 = new ConstructorClass("Kevin",20);
emp1.print();
Hope this helped, Enjoy :)

The type of the expression must be an array type but it resolved to

Im new to java. I dont understand why these errors are occurring. trying to make an array list so that it saves each object. The errors im getting are The type of the expression must be an array type but it resolved to ArrayList on the line 'newbug1[i].setspecies();'
Thankyou in advance
import javax.swing.JOptionPane;
import java.util.ArrayList;
public class Abug2 {
private String species;
private String name;
private char symbol = '\0';
private int horposition = 0, verposition = 0, energy = 0, uniqueID = 1, counter;
public Abug2(String species, String name, char symbol)
{
uniqueID = counter;
counter++;
}
public void setspecies(){
species = JOptionPane.showInputDialog(null, "Enter the species: ");
}
public String getspecies(){
return species;
}
public void setname(){
name = JOptionPane.showInputDialog(null, "Enter the name: ");
}
public String getname(){
return name;
}
public void setsymbol(){
symbol = name.charAt(0);
}
public char getsymbol(){
return symbol;
}
public int getid(){
return uniqueID;
}
public int gethorizontal(){
return horposition;
}
public int getvertical(){
return verposition;
}
public int getenergy(){
return energy;
}
//The class ABug has a set of methods: two or more constructors, toString, toText, and getters and setters for the attributes
public String toString(){
String tostring = "\nName: " + name + "\nHorizontal Position: " + horposition + "\nVertical Position: " + verposition + "\n";
return tostring;
}
public String toText(){
String totext = getspecies() + getname() + getsymbol() + getid() + gethorizontal() + getvertical() + getenergy();
return totext;
}
public static void main (String [] args){
ArrayList<Abug2> newbug1 = new ArrayList<Abug2>();
String choice = JOptionPane.showInputDialog(null, "Would you like to add another bug?: ");
do{for (int i = 0; i < 3; i++) {
newbug1.add(new Abug2("Bug", "Spider", 's'));
newbug1[i].setspecies();
newbug1[i].setname();
newbug1[i].setsymbol();
System.out.println(newbug1[i].toString());
} }while(choice != "yes");
}
}

For arraylists use get() instead:
newbug1.get(i).setspecies();
newbug1.get(i).setname();
newbug1.get(i).setsymbol();
Because it stores object references any setFoo calls affect the original object referenced in the arraylist.

In order to access an element in an ArrayList you have to use a method called get.
In your code, replace newbug1[i] by newbug1.get(i)
And moreover, you should store that reference in a variable instead of recalling it again and again:
Abug2 currentBug = newbug1.get(i);
currentBug.setSpecies();
Your code will gain in clarity.