"==" operator role

1, for comparison of basic data types

2. Determine if the reference points to the same block address of the heap memory.

Equals location:

In the Object class, and Object is the parent class of all classes, included in jdk, but not suitable for most scenarios, usually need to be rewritten

    public boolean equals(Object obj) {
            return (this == obj);
        }

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The role of equals:

Used to determine whether two variables are references to the same object, that is, whether the contents of the heap are the same, and the return value is a Boolean type.

Basic use of equals:

boolean b = obj1.equals(obj2);

The String type compares whether the contents of different objects are the same. You should use equals because == has different functions for comparing reference types and comparing basic data types.

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analyse as below:

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String is used as an object

Example 1: The object is different, the content is the same, "==" returns false, equals returns true

String s1 = new String("java");
String s2 = new String("java");

System.out.println(s1==s2);            //false
System.out.println(s1.equals(s2));    //true

Example 2: The same object, "==" and equals the same result

String s1 = new String("java");
String s2 = s1;

System.out.println(s1==s2);            //true
System.out.println(s1.equals(s2));    //true

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String is used as a basic type

If the values ​​are not the same, the objects are not the same, so "==" is the same as the equals result

String s1 = "java";
String s2 = "java";

System.out.println(s1==s2);            //true
System.out.println(s1.equals(s2));    //true

If there is no String object in the String buffer pool with the same value as the specified value, then the virtual machine will create a new String object for this purpose and store it in the String buffer pool.

If the String buffer pool has a String object with the same value as the specified value, then the virtual machine will not create a new String object for this purpose, but directly returns a reference to the existing String object.