Pointers in Miranda

public class Pointers {
    // We'll show how references work in contrast to values with
    // 2 methods: `zeroval` and `zeroref`. `zeroval` has an
    // `int` parameter, so arguments will be passed to it by
    // value. `zeroval` will get a copy of `ival` distinct
    // from the one in the calling method.
    public static void zeroval(int ival) {
        ival = 0;
    }

    // `zeroref` in contrast has an `Integer` parameter, which is an object
    // reference in Java. Modifying the object will affect the original
    // reference.
    public static void zeroref(Integer iref) {
        iref = 0;
    }

    public static void main(String[] args) {
        int i = 1;
        System.out.println("initial: " + i);

        zeroval(i);
        System.out.println("zeroval: " + i);

        // In Java, we use Integer wrapper class to simulate pointer-like behavior
        Integer iWrapper = new Integer(i);
        zeroref(iWrapper);
        i = iWrapper; // Unbox the Integer back to int
        System.out.println("zeroref: " + i);

        // Java doesn't have direct pointer manipulation, but we can print object identities
        System.out.println("object identity: " + System.identityHashCode(iWrapper));
    }
}

Java doesn’t have pointers in the same way as some other languages, but it does use references for objects. In this example, we’ve adapted the concept to show how Java handles value types (primitives) and reference types (objects).

zeroval doesn’t change the i in main, but zeroref does because it has a reference to the Integer object.

To run the program, compile it and then use java:

$ javac Pointers.java
$ java Pointers
initial: 1
zeroval: 1
zeroref: 0
object identity: 366712642

Note that the zeroval method doesn’t affect the original value, while zeroref does change it. The last line prints the object’s identity hash code, which is somewhat analogous to a memory address in languages with explicit pointers.

In Java, primitives are passed by value, while objects are passed by reference. The Integer class is used here to wrap the int primitive, allowing us to simulate pointer-like behavior.

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Pointers in Miranda