java-control-flow

Programs rarely execute in a straight line from start to finish. They need to make decisions based on conditions — handle different inputs, validate states, choose between algorithms. Without control flow constructs, every program would be a single fixed sequence of operations.

Java provides decision-making constructs that allow the program to execute different code paths based on boolean conditions. The primary constructs are if, if-else, if-else if-else chains, and switch statements. These evaluate a condition and branch to the matching code block.

The if statement evaluates a boolean expression. If true, the associated block executes; if false, execution moves to the else block (if present) or continues after the if construct. The switch statement evaluates an expression and jumps to the matching case label using a jump table (or lookup switch in the JVM). Each case must end with break to prevent fall-through.

• Boolean-only conditions: Unlike C/C++, only boolean expressions are valid in conditions
• Switch supports: int, char, String (Java 7+), and enums
• Enhanced switch (Java 14+): Arrow syntax with no fall-through
• Ternary operator: condition ? valueIfTrue : valueIfFalse as an expression

• Built from: Java Operators — relational and logical operators produce the boolean conditions
• Builds into: Java Loops — loops also use boolean conditions for termination
• Contrasts with: Java Loops — branching (if-else) vs repetition (loops) are complementary control structures
• Related: Java Methods — methods encapsulate control flow into reusable units

• Dangling else: else binds to the nearest unmatched if
• Switch fall-through: Missing break causes execution to continue into the next case
• String switch compiles differently: JVM uses hashCode + equals under the hood
• Ternary nesting: Nested ternaries reduce readability — prefer if-else for complex conditions