GenericsInterface.java

// A generic interface example.
// A generic containment interface.
// This interface implies that an implementing class contains one or more values.
interface Containment<T> {
    // The contains() method tests if a specific item is contained within
    // an object that implements Containment.
    boolean contains(T o);
}
// Implement Containment using an array to hold the values.
class MyClass<T> implements Containment<T> {
    T[] arrayRef;

    MyClass(T[] o) {
        arrayRef = o;
    }

    // Implement contains().
    public boolean contains(T o) {
        for(T x : arrayRef)
            if(x.equals(o)) return true;
        return false;
    }
}

public class GenericsInterface {
    public static void main(String[] args) {
        Integer[] x = { 1, 2, 3 };
        MyClass<Integer> ob = new MyClass<Integer>(x);
        if(ob.contains(2))
            System.out.println("2 is in ob");
        else
            System.out.println("2 is NOT in ob");
        if(ob.contains(5))
            System.out.println("5 is in ob");
        else
            System.out.println("5 is NOT in ob");

        // The following is illegal because ob
        // is an Integer Containment and 9.25 is
        // a Double value.
        // if(ob.contains(9.25)) // Illegal!
        // System.out.println("9.25 is in ob");
    }
}