[JAVA] Character string comparison: I was caught in the skill check problem of Paiza

I was caught in the skill check problem "character string comparison" (* problem of code disclosure OK) published in Paiza, so I summarized it.

The content of the problem is "Compare the two entered strings"

Reason for getting caught

I knew that there was a string comparison function, but the video I referred to didn't show how to do it, so I had a preconceived notion that I wouldn't use it.

Incorrect code

import java.util.*;

public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String line1 = sc.nextLine();
        String line2 = sc.nextLine();
              
        if( line1 == line2 ){
           System.out.println("OK"); 
        }
        else{
           System.out.println("NG"); 
        }
        
    }
}

Even if the output result is the same character string, "NG"

Enter the code below to confirm

Try debugging

import java.util.*;


public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String line1 = sc.nextLine();
        String line2 = sc.nextLine();
        
        //Check if statement
        String line1 = "moji";
        String line2 = "moji";

        //Confirmation of input
        System.out.println(line1);
        System.out.println(line2);
        
        if( line1 == line2 ){
           System.out.println("OK"); 
        }
        else{
           System.out.println("NG"); 
        }
        
    }
}

Output result;
moji
moji
ok

There is no problem with getting the if statement and character input. After all, I think that the character string comparison is bad (condition of if statement) and confirm it, and arrive at the following site. [Introduction to Java] How to compare strings (String) ("==" and "equals") Regarding the equality comparison of String type in Java

Correct code

import java.util.*;


public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String line1 = sc.nextLine();
        String line2 = sc.nextLine();
        
        if( line1.equals(line2)){
           System.out.println("OK"); 
        }
        else{
           System.out.println("NG"); 
        }
        
    }
}