String Methods

The Big Picture

String methods transform, search, and extract text. Strings are immutable: methods never change the receiver.

• length(), charAt(), substring() - basics
• contains(), indexOf(), startsWith() - searching
• toUpperCase(), trim(), replace() - transforms

String has 60+ methods - learn the top 10, look up the rest.

How It Works

Simple methods are O(n) or better; regex methods cost more.

• substring() creates a new String (since Java 7u6)
• split() uses regex - can be slow for simple delimiters
• matches() compiles regex each call - cache Pattern
• join() for delimited text; repeated assembly use StringBuilder
• chars() returns IntStream for functional processing

In the Java Landscape

String methods grew with each Java version.

• Java 8: String.join() for joining with delimiter
• Java 11: strip() (Unicode-aware), isBlank(), repeat()
• Java 12: indent(), transform()
• Apache StringUtils fills gaps: null-safe, padding, abbreviation
• Regex: Pattern and Matcher for complex text processing

Pitfalls and Best Practices

• Use strip() not trim() (handles Unicode whitespace)
• equalsIgnoreCase() for case-insensitive comparison
• isEmpty() checks length 0; isBlank() checks whitespace only
• Chain carefully - null at any point throws NPE
• Cache compiled Pattern objects for repeated regex use
• Use replace() for literal, replaceAll() for regex