Strings

The Big Picture

Strings represent immutable text in Java.

• The most commonly used type after int
• Objects, not primitives - stored on the heap
• Literal syntax: "Hello" creates a String object
• Immutable - original never changes; transform→new String, query→int/char/bool

Used everywhere: user input, file content, network data.

How It Works

Strings are backed by a char[] (Java 8) or byte[] (Java 9+). Because they're immutable, they're thread-safe and cacheable.

• result += part in a loop builds a new String each time (literals are folded)
• StringBuilder is mutable - use for building strings in loops
• String pool caches literals to save memory
• equals() compares content; == compares references

In the Java Landscape

Strings evolved significantly across Java versions.

• Java 9: compact strings (Latin-1 uses 1 byte per char)
• Java 11: isBlank(), strip(), lines(), repeat()
• Java 15: text blocks (preview in 13/14) with triple quotes """..."""
• Java 15: formatted() instance method
• StringBuffer is thread-safe but slower than StringBuilder

Pitfalls and Best Practices

• Use equals() not == to compare string content
• Use StringBuilder for concatenation in loops
• Avoid new String("literal") - wastes memory
• Calling a method on a null reference throws NullPointerException; concatenation converts null to "null"
• Use String.format() or text blocks for complex strings
• Use equals() for content; intern() only for rare dedupe/symbol tables