Conditionals

A conditional statement lets a program make a decision. Instead of running every line of code in order every single time, a conditional runs a block of code only if a certain boolean expression evaluates to true.

The if Statement

The simplest conditional is the if statement, which runs a block of code only if its condition is true.

If Formula

if ([condition]) {
    [code to run if condition is true]
}

if (velocity > 5.0) {
    System.out.println("Moving fast!");
}

If velocity is greater than 5.0, the message is printed. Otherwise, the block is skipped entirely, and the program moves on to whatever comes after it.

The else Statement

An else block runs when the if condition is false, giving you a fallback path.

if (velocity > 5.0) {
    System.out.println("Moving fast!");
} else {
    System.out.println("Moving slow.");
}

The else if Statement

When there are more than two possible outcomes, else if can be chained onto an if statement to check additional conditions in order.

if (velocity > 10.0) {
    System.out.println("Very fast!");
} else if (velocity > 5.0) {
    System.out.println("Moving fast!");
} else {
    System.out.println("Moving slow.");
}

Java checks each condition from top to bottom and runs the first block whose condition is true, skipping the rest. If none of the conditions are true, the final else block runs (if one exists).

Conditions are Boolean Expressions

The condition inside the parentheses of an if statement must always evaluate to a boolean. This means anything covered in the Expressions and Operators sections, such as relational and logical expressions, can be used here.

boolean hasNote = true;
boolean isAligned = true;

if (hasNote && isAligned) {
    System.out.println("Ready to shoot!");
}

For more information about building boolean expressions, see the Expressions and Operators sections.

Nested Conditionals

Conditionals can be placed inside other conditionals, allowing a program to check a second condition only after the first one has already been satisfied.

if (hasNote) {
    if (isAligned) {
        System.out.println("Ready to shoot!");
    } else {
        System.out.println("Aligning...");
    }
} else {
    System.out.println("No note detected.");
}

While nesting is sometimes necessary, deeply nested conditionals can be hard to read. Combining conditions with logical operators (&&, ||) is often a cleaner alternative when possible.

Braces and Style

Technically, Java allows you to omit curly braces {} around a single-line if body. However, FRC 190 always uses braces, even for one-line blocks:

// Avoid
if (velocity > 5.0)
    System.out.println("Moving fast!");

// Preferred
if (velocity > 5.0) {
    System.out.println("Moving fast!");
}

This prevents a very common bug where a second line is accidentally assumed to be part of the conditional, when it actually always runs regardless of the condition.