Does Java have something like C#'s ref and out keywords?

Question

Something like the following:

ref example:

void changeString(ref String str) {
    str = \"def\";
}

void main() {
    String abc = \"abc\";
    chan         


        

Answer 1

Actually there is neither ref nor out keyword equivalent in Java language as far as I know. However I've just transformed a C# code into Java that uses out parameter and will advise what I've just done. You should wrap whatever object into a wrapper class and pass the values wrapped in wrapper object instance as follows;

A Simple Example For Using Wrapper

Here is the Wrapper Class;

public class Wrapper {
    public Object ref1; // use this as ref
    public Object ref2; // use this as out

    public Wrapper(Object ref1) {
        this.ref1 = ref1;
    }
}

And here is the test code;

public class Test {

    public static void main(String[] args) {
        String abc = "abc";
        changeString(abc);
        System.out.println("Initial object: " + abc); //wont print "def"

        Wrapper w = new Wrapper(abc);
        changeStringWithWrapper(w);
        System.out.println("Updated object: " + w.ref1);
        System.out.println("Out     object: " + w.ref2);
    }

    // This won't work
    public static void changeString(String str) {
        str = "def";
    }

    // This will work
    public static void changeStringWithWrapper(Wrapper w) {
        w.ref1 = "def";
        w.ref2 = "And this should be used as out!";
    }

}

A Real World Example

A C#.NET method using out parameter

Here there is a C#.NET method that is using out keyword;

public bool Contains(T value)
{
    BinaryTreeNode parent;
    return FindWithParent(value, out parent) != null;
}

private BinaryTreeNode FindWithParent(T value, out BinaryTreeNode parent)
{
    BinaryTreeNode current = _head;
    parent = null;

    while(current != null)
    {
        int result = current.CompareTo(value);

        if (result > 0)
        {
            parent = current;
            current = current.Left;
        }
        else if (result < 0)
        {
            parent = current;
            current = current.Right;
        }
        else
        {
            break;
        }
    }

    return current;
}

Java Equivalent of the C# code that is using the out parameter

And the Java equivalent of this method with the help of wrapper class is as follows;

public boolean contains(T value) {
    BinaryTreeNodeGeneration result = findWithParent(value);

    return (result != null);
}

private BinaryTreeNodeGeneration findWithParent(T value) {
    BinaryTreeNode current = head;
    BinaryTreeNode parent = null;
    BinaryTreeNodeGeneration resultGeneration = new BinaryTreeNodeGeneration();
    resultGeneration.setParentNode(null);

    while(current != null) {
        int result = current.compareTo(value);

        if(result >0) {
            parent = current;
            current = current.left;
        } else if(result < 0) {
            parent = current;
            current = current.right;
        } else {
            break;
        }
    }

    resultGeneration.setChildNode(current);
    resultGeneration.setParentNode(parent);

    return resultGeneration;
}

Wrapper Class

And the wrapper class used in this Java code is as below;

public class BinaryTreeNodeGeneration>  {

    private BinaryTreeNode   parentNode;
    private BinaryTreeNode   childNode;

    public BinaryTreeNodeGeneration() {
        this.parentNode = null;
        this.childNode = null;
    }

    public BinaryTreeNode getParentNode() {
        return parentNode;
    }

    public void setParentNode(BinaryTreeNode parentNode) {
        this.parentNode = parentNode;
    }

    public BinaryTreeNode getChildNode() {
        return childNode;
    }

    public void setChildNode(BinaryTreeNode childNode) {
        this.childNode = childNode;
    }

}