if(this==otherObject) return true;

if(otherObject==null) return false;

if(getClass()!=otherObject.getClass()) return false;

if(!(otherObject instanceof ClassName)) return false;

ClassName other=(ClassName)otherObject;

return field1==other.field1&&field2.equals(other.field2)

String a = "abc"; 
String b = "abc"; 
String c = new String("abc"); 
String d = new String("abc"); 
System.out.println(a == b); // true 因为JAVA中字符串常量是共享的，只有一个拷贝 
System.out.println(a == c); // false a和c属于2个不同的对象 
System.out.println(a.equals(c)); // true 由于String对象的equals方法比较的是对象中的值，所以返回true。(和Object的equals方法不同) 
System.out.println(c==d); // false c和d虽然对象内的值相同，但属于2个不同的对象，所以不相等 
System.out.println(c.equals(d)); // true 

package chapter05.EqualsTest; 
 
import java.util.*; 
 
public class EqualsTest { 
 public static void main(String[] args) { 
  Employee alice1 = new Employee("Alice Adams", 75000, 1987, 12, 15); 
  Employee alice2 = alice1; // reference the same object 
  Employee alice3 = new Employee("Alice Adams", 75000, 1987, 12, 15); 
  Employee bob = new Employee("Bob Brandson", 50000, 1989, 10, 1); 
 
  System.out.println("alice1 == alice2: " + (alice1 == alice2)); 
 
  System.out.println("alice1 == alice3: " + (alice1 == alice3)); 
 
  System.out.println("alice1.equals(alice3): " + (alice1.equals(alice3))); 
 
  System.out.println("alice1.equals(bob): " + (alice1.equals(bob))); 
 
  System.out.println(bob.toString()); 
 } 
} 
 
class Employee { 
 public Employee(String n, double s, int year, int month, int day) { 
  name = n; 
  salary = s; 
  GregorianCalendar calendar = new GregorianCalendar(year, month, day); 
  hireDay = calendar.getTime(); 
 } 
 
 public String getName() { 
  return name; 
 } 
 
 public double getSalary() { 
  return salary; 
 } 
 
 public Date getHireDay() { 
  return hireDay; 
 } 
 
 public void raiseSalary(double byPercent) { 
  double raise = salary * byPercent / 100; 
  salary += raise; 
 } 
 
 @Override 
 public boolean equals(Object otherObject) { 
  // a quick test to see if the objects are identical 
  if (this == otherObject) 
   return true; 
 
  // must return false if the explicit parameter is null 
  if (otherObject == null) 
   return false; 
 
  // if the classed don't match,they can't be equal 
  if (getClass() != otherObject.getClass()) 
   return false; 
 
  // now we know otherObject is a non-null Employee 
  Employee other = (Employee) otherObject; 
 
  // test whether the fields hava identical values 
  return name.equals(other.name) && salary == other.salary 
    && hireDay.equals(other.hireDay); 
 
 } 
 
 @Override 
 public int hashCode() { 
  return 7 * name.hashCode() + 11 * new Double(salary).hashCode() + 13 
    * hireDay.hashCode(); 
 } 
 
 @Override 
 public String toString() { 
  return getClass().getName() + "[name=" + name + ",salary=" + salary 
    + ",hireDay=" + hireDay + "]"; 
 } 
 
 private String name; 
 private double salary; 
 private Date hireDay; 
} 
 
class Manager extends Employee { 
 public Manager(String n, double s, int year, int month, int day) { 
  super(n, s, year, month, day); 
  bouns = 0; 
 } 
 
 @Override 
 public double getSalary() { 
  double baseSalary = super.getSalary(); 
  return baseSalary + bouns; 
 } 
 
 public void setBouns(double b) { 
  bouns = b; 
 } 
 
 @Override 
 public boolean equals(Object otherObject) { 
  if (!super.equals(otherObject)) 
   return false; 
  Manager other = (Manager) otherObject; 
  // super equals checked that this and other belong to the same class 
  return bouns == other.bouns; 
 } 
 
 @Override 
 public int hashCode() { 
  return super.hashCode() + 17 * new Double(bouns).hashCode(); 
 } 
 
 @Override 
 public String toString() { 
  return super.toString() + "[bouns=" + bouns + "]"; 
 } 
 
 private double bouns; 
} 

import java.util.*;
import java.lang.Comparable;

/**
 * @desc equals()的测试程序。

 */
public class EqualsTest1{

 public static void main(String[] args) {
  // 新建2个相同内容的Person对象，
  // 再用equals比较它们是否相等
  Person p1 = new Person("eee", 100);
  Person p2 = new Person("eee", 100);
  System.out.printf("%s\n", p1.equals(p2));
 }

 /**
  * @desc Person类。
  */
 private static class Person {
  int age;
  String name;

  public Person(String name, int age) {
   this.name = name;
   this.age = age;
  }

  public String toString() {
   return name + " - " +age;
  }
 }
}

import java.util.*;
import java.lang.Comparable;

/**
 * @desc equals()的测试程序。
 */
public class EqualsTest2{

 public static void main(String[] args) {
  // 新建2个相同内容的Person对象，
  // 再用equals比较它们是否相等
  Person p1 = new Person("eee", 100);
  Person p2 = new Person("eee", 100);
  System.out.printf("%s\n", p1.equals(p2));
 }

 /**
  * @desc Person类。
  */
 private static class Person {
  int age;
  String name;

  public Person(String name, int age) {
   this.name = name;
   this.age = age;
  }

  public String toString() {
   return name + " - " +age;
  }

  /** 
   * @desc 覆盖equals方法 
   */ 
  @Override
  public boolean equals(Object obj){ 
   if(obj == null){ 
    return false; 
   } 

   //如果是同一个对象返回true，反之返回false 
   if(this == obj){ 
    return true; 
   } 

   //判断是否类型相同 
   if(this.getClass() != obj.getClass()){ 
    return false; 
   } 

   Person person = (Person)obj; 
   return name.equals(person.name) && age==person.age; 
  } 
 }
}

import java.util.*;
import java.lang.Comparable;

/**
 * @desc equals()的测试程序。
 */
public class EqualsTest3{

 public static void main(String[] args) {
  // 新建2个相同内容的Person对象，
  // 再用equals比较它们是否相等
  Person p1 = new Person("eee", 100);
  Person p2 = new Person("eee", 100);
  System.out.printf("p1.equals(p2) : %s\n", p1.equals(p2));
  System.out.printf("p1==p2 : %s\n", p1==p2);
 }

 /**
  * @desc Person类。
  */
 private static class Person {
  int age;
  String name;

  public Person(String name, int age) {
   this.name = name;
   this.age = age;
  }

  public String toString() {
   return name + " - " +age;
  }

  /** 
   * @desc 覆盖equals方法 
   */ 
  @Override
  public boolean equals(Object obj){ 
   if(obj == null){ 
    return false; 
   } 

   //如果是同一个对象返回true，反之返回false 
   if(this == obj){ 
    return true; 
   } 

   //判断是否类型相同 
   if(this.getClass() != obj.getClass()){ 
    return false; 
   } 

   Person person = (Person)obj; 
   return name.equals(person.name) && age==person.age; 
  } 
 }
}

p1.equals(p2) : true
p1==p2 : false