Comparing Strings: equals, not ==

The golden rule

To check if two strings have the same text, use .equals():

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String password = sc.nextLine();
        System.out.println(password.equals("secret123"));
        System.out.println(password == "secret123");
    }
}

Input (what the user types)

secret123

Output

true
false

The text matches, but == said false!

Think of it like this: == asks “are these the very same piece of paper?”. .equals() asks “do these two pieces of paper have the same words written on them?”. Usually you care about the words.

Remember: Compare numbers with ==. Compare Strings with .equals().

Ignoring capital letters

public class Main {
    public static void main(String[] args) {
        String answer = "YES";
        System.out.println(answer.equals("yes"));
        System.out.println(answer.equalsIgnoreCase("yes"));
    }
}

Output

false
true

Alphabetical order: compareTo

a.compareTo(b) gives a number: negative if a comes first in the dictionary, 0 if they're equal, positive if a comes after:

public class Main {
    public static void main(String[] args) {
        System.out.println("apple".compareTo("banana") < 0);
        System.out.println("cat".compareTo("cat"));
        System.out.println("zoo".compareTo("ant") > 0);
    }
}

Output

true
0
true

Strings never change

String methods don't change the original string. They give you a new one. Strings in Java are immutable (can't be changed):

public class Main {
    public static void main(String[] args) {
        String name = "ravi";
        name.toUpperCase();
        System.out.println(name);
        name = name.toUpperCase();
        System.out.println(name);
    }
}

Output

ravi
RAVI

Common mistake: Calling name.toUpperCase(); on its own does nothing useful – store the result: name = name.toUpperCase();