Combine 2 user inputs with a if/else if statement [duplicate]

This question already has an answer here:

• How do I compare strings in Java? 23 answers

I am very new to java. I am wanting to combine 2 user inputs and output an answer using if statement. This is what I have so far and it just skips straight to the end. What am I doing wrong? And is there a better way of doing this?

import java.util.*;

class ifelse {

    public static void main(String[] args) {

        Scanner user_input = new Scanner(System.in);

        String first_item;
        System.out.print("Enter Item: ");
        first_item = user_input.next();

        String second_item;
        System.out.print("Enter Item: ");
        second_item = user_input.next();

        String item_3;
        item_3 = (first_item + " " + second_item);

        if(item_3 == "blue yellow"){
            System.out.println("green");
        }
        else if(item_3 == "yellow blue"){
            System.out.println("green 3.0");
        }
        else{
            System.out.println("your dumb");
        }
    }
}