1 public class Client {
 2     public static void main(String[] args) {
 3          Employee e1 = new Employee("张三",100);
 4          Employee e2 = new Employee("张三",1001);
 5          Person p1 = new Person("张三");
 6          System.out.println(p1.equals(e1));
 7          System.out.println(p1.equals(e2));
 8          System.out.println(e1.equals(e2));
 9     }
10 }
11
12 class Person{
13     private String name;
14
15     public Person(String _name){
16        name = _name;
17     }
18
19     @Override
20     public boolean equals(Object obj) {
21          if(obj instanceof Person){
22            Person p = (Person) obj;
23            return name.equalsIgnoreCase(p.getName().trim());
24          }
25          return false;
26     }
27
28     public String getName() {
29         return name;
30     }
31
32     public void setName(String name) {
33         this.name = name;
34     }
35 }
36
37 class Employee extends Person{
38     private int id;
39     /*id的getter/setter方法省略*/
40     public Employee(String _name,int _id) {
41          super(_name);
42          id = _id;
43     }
44
45     public int getId() {
46         return id;
47     }
48
49     public void setId(int id) {
50         this.id = id;
51     }
52
53     @Override
54     public boolean equals(Object obj) {
55          if(obj instanceof Employee){
56            Employee e = (Employee) obj;
57            return super.equals(obj)&& e.getId() == id;
58          }
59          return false;
60     }
61 } 

true
true
false

 1 public boolean equals(Object obj) {
 2      if(obj!=null && obj.getClass() == this.getClass()){
 3         Person p = (Person) obj;
 4         if(p.getName()==null || name==null){
 5             return false;
 6         }else{
 7             return name.equalsIgnoreCase(p.getName());
 8         }
 9      }
10      return false;
11 }