aktuelle.kurse/m411/docs/Daten-Uebungen-CodeBeispiele/HashMap/Point3D.java

package m411;

import java.util.HashMap;

/**
 * @author pius portmann, 07.01.2020
 */
public class Point3D {
	
	private int x, y, z; // the coordinates
	
	public Point3D() {
		x = 0; y = 0; z = 0;
	}
	public Point3D(int x, int y, int z) {
		this.x = x;
		this.y = y;
		this.z = z;
	}
	
	@Override
	public boolean equals(Object obj) {
		System.out.println("equals() called"); // for debugging purposes
		if (!(obj instanceof Point3D))
			return false;
		Point3D p = (Point3D)obj;
		if (x != p.x || p.y != y || p.z != z)
			return false;
		return true;
	}

	@Override
	public int hashCode() {
		// Just one of many possibilites for a hash code calculation
		System.out.println("hashCode() called"); // for debugging purposes
		int hash = 0;
		hash = 61 * hash + x;
		hash = 61 * hash + y;
		hash = 61 * hash + z;
		return hash;
	}
	
	/** main method to test functionality */
	public static void main(String [] args) {
		// write out a few hash codes
		Point3D point;
		point = new Point3D();
		System.out.println( "hash=" + point.hashCode());
		point = new Point3D(1,0,0);
		System.out.println( "hash=" + point.hashCode());
		point = new Point3D(0,1,0);
		System.out.println( "hash=" + point.hashCode());
		point = new Point3D(0,0,1);
		System.out.println( "hash=" + point.hashCode());
		System.out.println();
		
		//check equality and identity
		Point3D p1 = new Point3D( 7, 5, 6);
		Point3D p2 = p1;                    // identical 
		Point3D p3 = new Point3D( 7, 5, 6); // equal
		System.out.println( "hash p1=" + p1.hashCode());
		System.out.println( "hash p2=" + p2.hashCode());
		System.out.println( "hash p3=" + p3.hashCode());	
		if (p1.equals(p2)) System.out.println("p1 equals p2");
		if (p2.equals(p3)) System.out.println("p2 equals p3");
		if (p1 == p2) System.out.println( "p1 is identical to p2");
		if (p1 == p3) System.out.println( "p1 is identical to p3");
		System.out.println();
				
		// Test usage in HashMap
		HashMap<Point3D,String> hmap = new HashMap();
		hmap.put(p1, "p1"); // stores p1
		hmap.put(p2, "p2"); // p2 replaces p1 becaus it's identical
		hmap.put(p3, "p3"); // p3 replaces p2 because it's equal
		System.out.println("--- hashMapsize=" + hmap.size());
		hmap.put(point, "point");
		System.out.println("--- hashMapsize=" + hmap.size());
		String v1 = hmap.get(p1);
		System.out.println("v1=" + v1);
		String vv = hmap.get(point);
		System.out.println("vv=" + vv);
	}
	
}