Simply understand = = and equals, why can string not use new

 public static void main(String[] args) {
        Car car1 = new Car();
        Car car2 = new Car();
        Car car3 = new Car();
        System.out.println(car1==car2);
        System.out.println(car1.equals(car2));
        String a = " Small ";
        String b = " Small ";
        System.out.println(a==b);
        System.out.println(a.equals(b));
}

false
false
true
true

== Compare memory addresses ,equals Is a comparison of the contents of the string .

The contents of entity type comparison need to be rewritten equals and hashcode() Method .

String Why not use new？

because jvm There is a string constant pool in

String a ="abc"; First jvm I will go to the constant pool to see if there is "abc" This string , If so, point to it , If not, open up a space in the constant pool to store abc

String a = new String("aba") This statement may create an object , It is also possible to create two objects .

establish 1 The case of an object , There is already a string in the constant pool aba, Because of the new Then you just need to create one in the heap String Object of type , then a Point to in constant pool aba

Creating two objects , except new Out of an object , Also create an object store in the constant pool aba, Then perform the assignment operation , take abn Assign a copy to the heap .