Java : Assume object reference or make copy
public class Point {
    public int x;
    public int y;

    public Point(int xVal, int yVal) {
        x = xVal;
        y = yVal;
    }

    public Point(Point pt) {
        x = pt.x;
        y = pt.y;
    }
}

public class BoundingBox {
    public Point topLeft;
    public Point bottomRight;

    public BoundingBox(Point setTopLeft, Point setBottomRight) {
        topLeft = new Point(setTopLeft);
        bottomRight = new Point(setBottomRight);
    }
}

Point topLeft = new Point(1, 2);
Point bottomRight = new Point(3, 4);
BoundingBox box = new BoundingBox(topLeft, bottomRight);

topLeft.x = 5; // Oops, this just changed box.topLeft.x

public class Point {
    public final int x;
    public final int y;

    public Point(int xVal, int yVal) {
        x = xVal;
        y = yVal;
    }

    public Point(Point pt) {
        x = pt.x;
        y = pt.y;
    }
}

public class MyClass {
           private Point foo;
           private Point bar;

           public MyClass(Point foo, Point bar) {
             this.foo = foo;
             this.bar = bar;
           }

           public Point foo() {
             return foo;
           }

           public Point bar() {
             return bar;
           }

           . . .

           //Seems harmless enough?
           //Lets destroy it
           Point foo = new Point(1 ,2);
           Point bar = new Point(3 ,4);
           MyClass mc = new MyClass(foo, bar);
           bar.x = 99; //<-- changes internal of mc!

//Fixed version!
            public MyClass(Point foo, Point bar) {
             this.foo = new Point(foo.getLocation());
             this.bar = new Point(bar.getLocation());
           }

           public Point foo() {
             return new Point(foo.getLocation());
           }

           public Point bar() {
             return new Point(bar.getLocation());
           }

           . . .