1. = =

== compares the values in the stack

  • Basic data types that directly compare variable values for equality;
  • Reference type, which compares the variable to the address of the memory object

2, equals

  • The equals method in Object also compares equals by default, and is usually overridden
public boolean equals(Object obj) {
        return this == obj;
}
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  • If the equals method is not overridden, it compares the address of the object to which the variable referring to the type refers

  • A class like String overrides equals to compare the contents of the objects to which it refers

public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj instanceof String) {
            String s = (String)obj;
            int i = value.length;
            if (i == s.value.length) {
                char ac[] = value;
                char ac1[] = s.value;
                for (int j = 0; i-- ! =0; j++)
                    if(ac[j] ! = ac1[j])return false;

                return true; }}return false;
    }
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3, test,

public class test {
     
     public static void main(String[] args) {
         String s1 = "hello";                // Create a new object in the string constant pool
         String s2 = "hello";                // "Hello" was found in the string constant pool, pointing to the object address
         String s3 = new String("hello");    // Create a new object in the heap and point to its address
         
         System.out.println(s1 == s2);       //true
         System.out.println(s1 == s3);       //false
         System.out.println(s1.equals(s2));  //true
         System.out.println(s1.equals(s3));  //true      }}Copy the code