import java.util.ArrayList;

public class ArrayListTester {

    public static void main(String args []){

        // create an ArrayList with a capacity of 20
        ArrayList<Integer> a = new ArrayList<Integer>(20);  
        System.out.println(a);
        a.add(10);
        System.out.println(a);         
        // can we do the following?
        a.add(0,5);
        System.out.println(a);         
        // how about:
        a.add(1,5);
        System.out.println(a);         
        // and let's try now:
        //a.add(10,5);

        // create some instances of StoresX
        StoresX x1 = new StoresX(42);
        StoresX x2 = new StoresX(10);
        StoresX x3 = new StoresX(10);
        // notice that x3 stores the same value as x2.
        // by overloading the standard java .equals method in
        // StoresX we get that
        System.out.println("x2 equals x3? " + x2.equals(x3));
        // evaluates to true
        // this isn't true using the default implementation of
        // .equals.  Why?

        ArrayList<StoresX> xarray = new ArrayList<StoresX>();
        xarray.add(x1);
        xarray.add(x2);
        // to check if there is an object like x3 in the ArrayList:
        System.out.println(xarray.indexOf(x3));
        // note that indexOf iteratively applies the .equals until
        // if finds an object that is identical to the given object
        // (identical under the definition provided by the .equals method).
    }
}
 

public class StoresX {
        private int x;

        public StoresX(int x){
                this.x = x;
        }

        public boolean equals(Object other){
                return this.x == ((StoresX)other).x;
        }

        public int getX() {
                return x;
        }

        public void setX(int x) {
                this.x = x;
        }

}