public boolean euqals(Object obj){
 return this == obj;
}

public boolean equals(Object anObject) {
 if (this == anObject) {
 return true;
 }
 if (anObject instanceof String) {
 String anotherString = (String)anObject;
 int n = count;
 if (n == anotherString.count) {
  char v1[] = value;
  char v2[] = anotherString.value;
  int i = offset;
  int j = anotherString.offset;
  while (n– != 0) {
  if (v1[i++] != v2[j++])
   return false;
  }
  return true;
 }
 }
 return false;
}

public boolean equals(Object obj)

class Point{
final int x;
final int y;
public void Point(int x, int y)
 this.x = x;
 this.y = y;
}
public boolean euqals(Point obj){
  return (this.x == obj.x && this.y == obj.y);
 }
}

Point a(1, 2);
Poinr b(1, 2);
System.out.println(a.equals(b));// 输出true

import java.util.HashSet;

HashSet<Point> coll = new HashSet<Point>();
coll.add(a);
System.out.println(coll.contains(b));// 输出false

public class ColoredPoint extends Point { 
 private final Color color;
 public ColoredPoint(int x, int y, Color color) {
 super(x, y);
 this.color = color;
 }

 @Override 
 public boolean equals(Object other) {
 boolean result = false;
 if (other instanceof ColoredPoint) {
  ColoredPoint that = (ColoredPoint) other;
  result = (this.color.equals(that.color) && super.equals(that));
 }
 return result;
 }
}

Point p = new Point(1, 2);
ColoredPoint cp = new ColoredPoint(1, 2, Color.RED);
System.out.println(p.equals(cp)); //输出ture
System.out.println(cp.equals(p)); //输出false

@overwrite
public boolean equals(Object obj){
 if((obj instanceof Point)){
 return false;
 }

 if(!(obj instanceof ColoredPoint)){
 return obj.equals(this);
 }

 return super.equals(obj) && ((ColoredPoint)obj).color == color;
}

ColoredPoint cp1 = new ColoredPoint(1, 2, Color.RED);
Point p = new Point(1, 2);
ColoredPoint cp2 = new ColoredPoint(1, 2, Color.BLUE);
System.out.println(cp1.equals(p)); //true
System.out.println(p.equals(cp2)); //true
System.out.println(cp1.equals(cp2)); //false

class ColoredPoint{
 private final Point point;
 private final Color color;

 public Point asPoint(){
 return point;
 }

 public boolean equals(Object obj){
 boolean ret = false;
 if(obj instanceof ColoredPoint){
  ColoredPoint that = (ColoredPoint)obj;
  ret = that.point.equals(point) && color.equals(that.color);
 }
 return ret;
 }
}