Code demonstration:

public class Test {
    public static void main(String[] args){
        // Case 1
        String str1 = new String("hello");
        String str2 = "hello";
        System.out.println(str1 == str2);  // false
        System.out.println(str1.equals(str2));  // true
        
        // Case two
        String str3 = "world";
        String str4 = "world";
        System.out.println(str3 == str4);  // true
        System.out.println(str3.equals(str4));  // true
    }
}

 Problem Description:

•  " == " Its application scenarios are roughly divided into two categories,first kindIs used to compare basic data types( Java Eight basic data types: byte,short,int,float,long,double,char,boolean)，They compare values directly between the underlying data types.Second categoryIt is used to compare objects. It will directly compare two objectsMemory address，That is, unless two objects point to the same address, they are always false.
• equals()The method is Object Methods in the base class, so any class will inherit this method, but some classes override this method, such as String Class, we can combine String class equals()Source code to explain.

// Source code of the overridden equals() method in the String class:
    public boolean equals(Object anObject) {
        if (this == anObject) {  // First, judge whether it is the same object. If it is true, return it directly
            return true;
        }
        if (anObject instanceof String) {  // Then judge whether the instance passed in is a String. If so, continue to judge
            String anotherString = (String)anObject;
            int n = value.length;
            if (n == anotherString.value.length) {  // First, judge the length of two strings. If not equal, return false directly
                char v1[] = value;  // At the bottom of the string is an array of characters called value to load the data.
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) { 
                    if (v1[i] != v2[i])  // Compare each character for equality
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }