returning an object from a method

[bigj]

im currently reading a book and i want to clarify this,,

the value of an object is the reference , and when you return that object you are returning the value

my question is, AFTER you return a value(object) ,is the object deallocated from the memory?

[r035198x]

If by deallocated you mean garbage collected then probably not.
For the object to be garbage collected, there must be no live references to that object anymore and even then the garbage collector has to decide that it wants to run for that object to be collected.
If the caller assigns the return value to another variable then the object is still accessed from that reference and is not eligible for garbage collection.

P.S It is best not to mix too many issues when studying. i.e don't try to learn about garbage collection before you have finished with learning about methods.

[JosAH]

im currently reading a book and i want to clarify this,,

the value of an object is the reference , and when you return that object you are returning the value

my question is, AFTER you return a value(object) ,is the object deallocated from the memory?

Think of objects as television sets; your variables or parameters are the remote controls that 'point to' the television sets. You never have a television set, just the remote control. When you return an object from a method you return a remote control. When no control for a specific object exists anymore the television set (the object) is garbage collected but as long as at least one remote control exists the television set exists as well.

kind regards,

Jos

[bigj]

hmm tnx for the respone i think i should finish the chapter first, then ill post back to this topic as soon as possible for any furhter questions... tnx tnx,
anyway i dont have any knowledge about garbage collections yet... tnx:)

[bigj]

im currently studying the objects, refference, reserved word this..
and im trying to imitate the logic behind the equals method of the String class, i just want to ask the problem with my program here

public class EqualsString {

    private String word;
    
    public EqualsString(String word) {

        setTheWord(word);
    }
    
    public boolean equals(EqualsString string) {

        if (this.getTheWord() == string.getTheWord()) {

            return true;
        }
        else {

            return false;
        }
   }

    private void setTheWord(String word) {

        this.word = word;
    }

    public EqualsString getTheWord() {

        EqualsString str = new EqualsString(word);

        return str;
    }
}

main:

    public static void main(String[] args) {

        EqualsString name1 = new EqualsString("Equals");
        EqualsString name2 = new EqualsString("Equals");

        if (name1.equals(name2)) {

            System.out.println(true);
        }
        else {

            System.out.println(false);
        }
    }

why is the ouput false? :confused:

[r035198x]

Because you compared the Strings using == instead of using the equals method.

You did

if (this.getTheWord() == string.getTheWord())

Instead of

if (this.getTheWord().equals(string.getTheWord()))

You also didn't override the equals method correctly.
Read
Overriding the equals and hashCode methods - Java insights

[bigj]

about this one...

public class Operations {

    private int number;

    public Operations(int num) {

        setTheNumber(num);
    }

    private void setTheNumber(int number) {

        this.number = number;
    }

    public int getNumber() {

        return number;
    }
    
    public Operations add(Operations op) {
        
        int num1,
            num2;

        num1 = this.getNumber(); // refers to the receiving objects data members
        num2 = op.getNumber();   // refers to the argument object

        Operations sum = new Operations(num1 + num2);

        return sum;
    }

    public Operations subtract(Operations op) {

        int num1,
            num2;

        num1 = this.getNumber();
        num2 = op.getNumber();

        Operations difference = new Operations(num1 - num2);

        return difference;
    }
    
    // when i add this method
    public String toString() {

        return getNumber() + "" ;
    }
    
    public Operations divide(Operations op) {

        int num1,
            num2;

        num1 = this.getNumber();
        num2 = op.getNumber();

        if (num1 == 0 || num2 == 0) {

            System.err.print("Cannot Divide By Zero");
            System.exit(1);
        }

        Operations quotient = new Operations(num1 / num2);

        return quotient;
    }

    public Operations multiply(Operations op) {

        int num1,
            num2;

        num1 = this.getNumber();
        num2 = op.getNumber();
        
        Operations product = new Operations(num1 * num2);

        return product;
    }

    // Main
    public static void main(String[] args) {

        Operations num1,
                   num2;

        Operations sum,
                   diff,
                   quot,
                   prod;

        num1 = new Operations(10);
        num2 = new Operations(5);

        sum = num1.add(num2);
        diff = num1.subtract(num2);
        quot = num1.divide(num2);
        prod = num1.multiply(num2);

        System.out.println(sum);
        System.out.println(diff);
        System.out.println(quot);
        System.out.println(prod);
    }
}

when im not yet Overriding the toString() method the output is
this:

xxTestxx.Operations@3e25a5
xxTestxx.Operations@19821f
xxTestxx.Operations@addbf1
xxTestxx.Operations@42e816

but when i include the toString() method
the output became fine:

15
5
2
50

but i only added the toString() method... i didnt use this method in any of my predefined methods? how does it affects the correct output? :confused:

[r035198x]

When you pass a variable of reference type to println, it automatically calls toString on the object to get the string to print out.