Java-将值添加到另一个类的变量中

Question

My problem is how do I add a value to a variable from another class, for example:

private int balance;

then later in the methods in the same class, I add values to the balance with no problem using:

balance += 50;

but when I go to another class, and type the object then the setter for the balance:

myObject.setBalance(50);

but the problem strikes here, when I go to the first class and return the balance from there, i get nothing (or the old value of balance) in other words, the NEW value of balance is not being added. Any ideas why? I've been stuck at this point for the last couple of hours

Here's my code:

public class Zoo 
{
    private int balance;

    public void setBalance(int balance)
    {
        this.balance = balance;
    }

    public int getBalance()
    {
        return this.balance;
    }
}

MY SECOND CLASS:

public class RandomEvents
{
    private Zoo ZooBalance = new Zoo();

    public void callEventSix()
    {
        System.out.println("A local group has raised money to your Zoo");
        System.out.println("Would you like to accept the money? (y) or (n)");
        Scanner readerEventThree = new Scanner(System.in);
        String readerTwo = readerEventThree.next();
        if ( readerTwo.equals("y") ) 
        {
            ZooBalance.setBalance(166);
            System.out.println("You have accepted the gift");
            System.out.println("Your new balance is " + ZooBalance.getBalance());
        } else if ( readerTwo.equals("n") )
        {
            System.out.println("You have refused the gift");
        }
    }
}

Answer 1

In your case

Replace this line:

ZooBalance.setBalance(166);

with:

ZooBalance.setBalance(ZooBalance.getBalance() + 166);
Sytem.out.println(ZooBalance.getBalance()); // 166

You need to make a setter for that class. Assuming the name of the class is TestClass .

class TestClass {
    private int balance = 50;
};
public int getBalance() {
    return this.balance;
};
public void setBalance(int newBalance) {
    this.balance = newBalance;
};

And then in another class:

TestClass test = new TestClass();
test.setBalance(test.getBalance() + 50);
System.out.println(test.getBalance);// 100

Answer 2

I'm pretty sure there's a difference between adding 50 to a value and setting a value to 50 .

myObject.setBalance(50); will not add 50 , it will change the value to 50 . To add 50, you'd have to do something along the lines of myObject.setBalance(myObject.getBalance() + 50);

Answer 3

generally there are two ways to this.

First. Use getter and setter :

Zoo zoo = new Zoo();
zoo.setBalance(zoo.getBalance() + 50);

Second. Add an adder method:

public void addToBalance(int addend) {
    balance += addend;
}

Zoo zoo = new Zoo();
zoo.addToBalance(50);