public boolean equals(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) {
  return (obj instanceof Float)
      && (floatToIntBits(((Float)obj).value) == floatToIntBits(value));
  }

However, there are two exceptions:
If f1 and f2 both represent
Float.NaN, then the equals method returns
true, even though Float.NaN==Float.NaN
has the value false.
If <code>f1 represents +0.0f while
f2 represents -0.0f, or vice
versa, the equal test has the value
false, even though 0.0f==-0.0f
has the value true.

public class Person {
  protected String name;

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }
  
  public Person(String name){
    this.name = name;
  }
  
  public boolean equals(Object object){
    if(object instanceof Person){
      Person p = (Person) object;
      if(p.getName() == null || name == null){
        return false;
      }
      else{
        return name.equalsIgnoreCase(p.getName());
      }
    }
    return false;
  }
}

public class Employee extends Person{
  private int id;
  
  public int getId() {
    return id;
  }

  public void setId(int id) {
    this.id = id;
  }

  public Employee(String name,int id){
    super(name);
    this.id = id;
  }
  
  /**
   * 重写equals()方法
   */
  public boolean equals(Object object){
    if(object instanceof Employee){
      Employee e = (Employee) object;
      return super.equals(object) && e.getId() == id;
    }
    return false;
  }
}

public class Test {
  public static void main(String[] args) {
    Employee e1 = new Employee("chenssy", 23);
    Employee e2 = new Employee("chenssy", 24);
    Person p1 = new Person("chenssy");
    
    System.out.println(p1.equals(e1));
    System.out.println(p1.equals(e2));
    System.out.println(e1.equals(e2));
  }
}