Build it step by step

Every step below leaves a scenario that compiles and runs. If you stop halfway you will have something that works, not something broken. Follow along in Greenfoot rather than reading straight through.

1. Step 1

   On your screen An editor showing comparison expressions with their true or false results annotated.

   int score = 10;
   score > 5     // true
   score < 5     // false
   score == 10   // true
   score != 10   // false

   Each of these is a question, and the answer is always exactly true or false.

   `>` and `<` you already know. `==` asks "are these the same?". `!=` asks "are these different?".

   Note there is no `=` in that list at all.

2. Step 2

   On your screen A side-by-side comparison of a single equals and a double equals with their meanings labeled.

   score = 10;   // PUTS 10 into score
   score == 10;  // ASKS whether score is 10

   These look almost identical and do completely different things.

   One `=` is an instruction: change the box. Two `==` is a question: is the box holding this?

   Say it out loud when you read code. "Becomes" for one, "is equal to" for two. Using `=` where you meant `==` is the most common logic error in this entire course, and in a condition Java usually rejects it with `incompatible types`, which is its way of saying "you gave me an instruction where I wanted a question".

3. Step 3

   On your screen Two conditions combined with the and operator, showing the result is true only when both parts are true.

   boolean hasKey = true;
   int score = 10;
   
   hasKey && score > 5   // true, both are true
   hasKey && score > 50  // false, the second part fails

   `&&` is AND. Both sides must be true or the whole thing is false. One false anywhere poisons it.

   `||` is OR. It only needs one side to be true.

   The two vertical bars are on the backslash key on most keyboards.

4. Step 4

   On your screen The not operator inverting a boolean value.

   boolean gameOver = false;
   !gameOver             // true
   !gameOver && hasKey   // true

   `!` is NOT. It flips true to false and false to true.

   Read `!gameOver` as "not game over". Once you read it that way, `!gameOver && hasKey` is just "the game is not over and I have the key", which is a sentence rather than a puzzle.