package com.lk.C;class User { private String name; private int age; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public void setName(String name) { this.name = name; } public String getName() { return name; } public boolean equals(Object obj) { if(this == obj) { return true; } if(null == obj) { return false; } if(this.getClass() != obj.getClass()) { return false; } User user = (User) obj; if(this.name.equals(user.name)&&this.age == user.age) { return true; } return false; } } public class Test6 { public static void main(String[] args) { User userA = new User(); userA.setName("王明"); userA.setAge(10); User userB = new User(); userB.setName("王明"); userB.setAge(10); User userC = new User(); userC.setName("王亮"); userC.setAge(10); System.out.println("userA equals userB:" + userA.equals(userB)); System.out.println("userA equals userC:" + userA.equals(userC)); } }
userA equals userB:trueuserA equals userC:false
package com.lk.C;public class Test7 { public static void main(String[] args) { int a = 10; int b = 10; System.out.print("基本类型a==b:"); System.out.println(a == b); System.out.println("-----"); String s1 = "abc"; String s2 = "abc"; System.out.print("String类型是s1==s2:"); System.out.println(s1 == s2); System.out.println("-----"); String s3 = new String("abc"); String s4 = new String("abc");//可以看出==比较的是栈的地址是否相同 System.out.print("String类型用new String()是s1==s2:"); System.out.println(s3 == s4); System.out.println(s1 == s3); System.out.println("-----"); Integer i1 = 1; Integer i2 = 1; System.out.print("包装类型是i1==i2:"); System.out.println(i1 == i2); System.out.println("-----"); Integer i3 = 128; Integer i4 = 128;//此时输出false是因为Integer在-128-127之间会缓存,超出这个范围就不会缓存了 System.out.print("包装类型是i3==i4:"); System.out.println(i3 == i4); System.out.println("-----"); Integer i5 = new Integer("1"); Integer i6 = new Integer("1"); System.out.print("包装类型用new Integer()是i5==i6:"); System.out.println(i5 == i6);//用new Integer()多少都不会缓存 System.out.println("-----"); A a1 = new A(1); A a2 = new A(1); A a3 = a2; System.out.print("普通引用类型a1 == a2:"); System.out.println(a1 == a2); System.out.println(a2 == a3);//对象赋给新对象连地址都是相同的 System.out.println("-----"); }}class A{ int i; public A(int i){ this.i = i; }}
package com.lk.C;public class Test8 { public static void main(String[] args) { // TODO Auto-generated method stub System.out.println("基本类型没有equals方法"); System.out.println("-----"); String s1 = "abc"; String s2 = "abc"; System.out.print("String类型的equals方法:"); System.out.println(s1.equals(s2)); System.out.println("-----"); String s3 = new String("abc"); String s4 = new String("abc");//可以看出比较equals方法比较的是堆里的值是否相同 System.out.print("String类型的new String()的equals方法:"); System.out.println(s3.equals(s4)); System.out.println("-----"); System.out.print("String用==赋值和用new String()赋值的比较:"); System.out.println(s1.equals(s3)); System.out.println("-----"); Integer i1 = 1; Integer i2 = 1; System.out.print("包装类的equals方法:"); System.out.println(i1.equals(i2)); System.out.println("-----"); Integer i3 = new Integer(1); Integer i4 = new Integer(1); System.out.print("包装类的new Integer()用equals方法:"); System.out.println(i3.equals(i4)); System.out.println("-----"); System.out.print("Integer用==赋值和用new Integer()赋值的比较:"); System.out.println(i1.equals(i3)); System.out.println("-----"); }}
package com.lk.C;public class Test9 { public static void main(String[] args) { // TODO Auto-generated method stub Student s1 = new Student("阿坤",21); Student s2 = new Student("阿坤",21); Student s3 = new Student(); Student s4 = new Student(); Student s5 = s1; System.out.print("普通类对象的==非默认构造:"); System.out.println(s1 == s2); System.out.println(s1 == s5); System.out.println("-----"); System.out.print("普通类对象的equals非默认构造:"); System.out.println(s1.equals(s2)); System.out.println(s1.equals(s5)); System.out.println("-----"); System.out.print("普通类对象的==默认构造:"); System.out.println(s3 == s4); System.out.println("-----"); System.out.print("普通类对象的equals默认构造:"); System.out.println(s3.equals(s4)); System.out.println("-----"); System.out.print("对普通对象的属性进行比较equals:"); System.out.println(s1.name.equals(s2.name)); System.out.print("对普通对象的属性进行比较==:"); System.out.println(s1.name == s2.name); }}class Student{ public String name; public int age; public Student(){ } public Student(String name,int age){ this.name = name; this.age = age; } public void test(){ System.out.println(this.name); System.out.println(this.age); }}
java中,(1)对于字符串变量来说,equal比较的两边对象的内容,所以内容相同返回的是true。至于你没问到的“==”,比较的是内存中的首地址,所以如果不是同一个对象,“==”不会返回true 而是false。举个简单的例子,String s1="abc", s2="abc";String s3 =new String("abc");String s4=new String("abc");s1==s2 //true,s1.equals(s2) //true,s3.equals(s3) //true,equal比较的是内容s3==s4//false,==比较的是首地址,所以是false(2)对于非字符串变量,equals比较的内存的首地址,这时候和==是一样的,即比较两边指向的是不是同一个对象,即Sample sa1 = new Sample();Sample sa2 = new Sample();sa1.equals(sa2) //false,因为不是同一对象 注意,如果加上sa1=sa2;那么sa1.equals(sa2) //true
原标题:Java中==、equals、hashcode的区别与重写equals以及hashcode方法实例(转)
关键词:JAVA