Control Structures: if Statements & For Loops

if Statements: One-Way and Two-Way Selection

An if statement runs its body only when a boolean condition is true:

if (joystick.getRawButton(1))
{
    intake.spin(0.5);
}

Add an else for a second branch that runs when the condition is false:

if (joystick.getRawButton(1))
{
    intake.spin(0.5);
}
else
{
    intake.stop();
}

Always use curly braces, even for a single statement — Java doesn't require them, but skipping them is exactly how the classic "which statement is actually inside the if" bug happens.

The Classic `=` vs. `==` Mistake

One = assigns a value; two == test whether a value equals something. Writing if (isCold = true) inside a condition compiles (it's a legal assignment expression) but silently does the wrong thing — it assigns true to isCold and the condition is always true, regardless of what isCold was before.

For Loops: Three Parts, One Line

A for loop bundles the three steps of a loop — initialize, test, update — into one header:

for (int i = 0; i < sensors.length; i++)
{
    if (sensors[i].isFaulty())
    {
        report(sensors[i]);
    }
}

The three parts are always separated by semicolons, in this order: initialize the loop variable, test it, update it. Starting at 0 pairs naturally with <; starting at 1 pairs naturally with <= — pick whichever matches how many times you actually want to run.

Common Pitfalls

Missing curly braces. Without them, only the very next line is actually part of the if/loop body — everything after it runs unconditionally, every time.
= instead of == in a condition. A real, silent bug — the code compiles and the condition is always true.
Off-by-one in a for loop's bound. i < sensors.length visits every valid index; i <= sensors.length runs one iteration too many and reads past the end.

Key Takeaways

An if runs its body only when its condition is true; an else gives it a second branch for when it's false.
Always use curly braces around a conditional or loop body.
== tests equality; = assigns. Confusing them compiles but silently breaks the logic.
A for loop's header has three parts — initialize, test, update — always in that order, separated by semicolons.

Deck context: mechacoder-test/src/lessons/java-1.js, slide 5 ("CONTROL STRUCTURES")