Loops

The Big Picture

Loops repeat code until a condition changes.

• for: count-based iteration with known bounds
• while: condition-based, may not run at all
• do-while: runs at least once, then checks condition
• Enhanced for-each: for (var item : list)

Loops are the backbone of data processing in Java.

How It Works

The JVM compiles loops to jump instructions. Hot loops get JIT-compiled to native code with optimizations.

• break exits the loop, continue skips to next iteration
• Labeled breaks exit outer loops: outer: for (...)
• Collections: for-each uses an Iterator; arrays use indexed traversal
• Infinite loops: while(true) or for(;;)

In the Java Landscape

Modern Java offers functional alternatives to loops.

• Streams: list.stream().filter(...).map(...)
• forEach(): list.forEach(item -> process(item))
• IntStream.range(0, n) replaces index-based for loops
• Collections.nCopies() for repeated values
• Use loops for simple iteration, streams for transforms

Pitfalls and Best Practices

• Off-by-one: use < not <= for zero-based arrays
• Don't modify a collection while iterating with for-each
• Use Iterator.remove() or removeIf() instead
• Avoid infinite loops - ensure termination condition changes
• Prefer for-each over indexed for when index isn't needed
• Extract loop body into a method if longer than 10 lines