The difference between equals and ==-javaTutorial-php.cn

The difference between equals and ==

巴扎黑

Release： 2016-12-03 11:36:45

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equals is a method provided by object

equals is used to compare whether the variable values of two basic types are equal. If used in a reference type, it compares whether the two variables point to the same object.

equals and == in object They all compare whether the addresses are equal, and in String equals compares whether the values are equal.

equals compares whether the contents of the two blocking objects are equal, while == compares whether the values in the memory are equal.

equals does not Can be used to compare integer variables

The following is the code implementation:

//定义一个Student类
public class Student {
private int age;
 
public Student(int age) {
this.age = age;
}
public boolean equals(Object obj) {
if(this==obj){
return true;
}
if(obj instanceof Student){
Student st = (Student)obj;
return this.age==st.age;
}
return false;
}
}

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//定义一个Demo3主类，创建对象输出他们的结果并分析其原因
public class Demo3 {
public static void main(String[] args) {
Student s1 = new Student(100);
Student s2 = new Student(100);
Student s3 = s1;
System.out.println(s1==s2);
System.out.println(s1.equals(s2));
System.out.println(s1.equals(s3));
}
}

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//定义一个Demo类，分别用几种不同的方式给以下7个变量赋值，分析这几种方式有什么区别
public class Demo {
public static void main(String[] args) {
// 以下三种方式都是在内存中保存一个数值100
int a1 = 100;
int a2 = 100;
Integer a3 = 100;
Integer a4 = 100;
Integer a5 = new Integer(100);
Integer a6 = new Integer(100);
System.out.println(a1 == a2);
System.out.println(a3 == a4);
System.out.println(a1 == a3);
System.out.println(a5 == a6);
System.out.println(a1 == a5);
System.out.println(a3 == a5);
int a7 = a6;

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//定义一个Demo2主类，分别给变量赋值，分别用==和equals输出结果，看有什么不同并分析其原因
public class Demo2 {
public static void main(String[] args) {
String s1 = "ABC";
String s2 = "ABC";
String s3 = new String("ABC");
String s4 = new String("ABC");
System.out.println(s1 == s2);
System.out.println(s3 == s4);
System.out.println(s1 == s3);
System.out.println("-------------------------");
System.out.println(s1.equals(s2));
System.out.println(s3.equals(s4));
System.out.println(s1.equals(s3));
}
}

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