Chapter 3: Strings in Java

In Java, strings are first-class immutable objects backed by special JVM memory regions. Understanding String immutability, the String Constant Pool (SCP), mutable string builders, and modern compact string representation is essential for writing memory-efficient, performant enterprise code.

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🧭 Subtopics & Curriculum

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Memory Optimization3.1

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3.1 String Immutability & the String Pool

• What is a String in Java?
• Two ways to create a String
  • Method 1: String literal
  • Method 2: Using new
  • Important
• What is String Pool?
• Why is String immutable?
• Why is String immutable?
  • 1. String Pool
  • 2. Security
  • 3. Thread safety
  • 4. HashMap / HashSet
  • 5. == vs equals()
• What happens with +?
• Example of String Constant Pool Memory Model

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Performance & Mutability3.2

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3.2 String vs StringBuilder vs StringBuffer

• StringBuilder
• StringBuffer
• Major Differences
• String vs StringBuilder vs StringBuffer

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Equality & Interning3.3

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3.3 String Equality & .intern() Mechanics

• == vs .equals() vs .compareTo()
• Compile-Time Literal Folding
• .intern()
• Common String methods
  • length()
  • charAt()
  • substring()
  • toUpperCase() / toLowerCase()
  • equals() vs equalsIgnoreCase()
  • compareTo()
• String and final

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Standard API3.4

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3.4 Essential Modern String Methods

• 1. Modern String Inspection (Java 11+)
• 2. Advanced Whitespace Stripping: strip() vs trim()
• 3. Transformations & Multi-line Operations

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Modern JVM Features3.5

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3.5 Text Blocks & Compact Strings

• 1. Text Blocks (Java 15 LTS)
  • Incidental Whitespace Stripping
  • Escape Sequences in Text Blocks
• 2. Compact Strings (Java 9 JVM Optimization)
  • The Compact Strings Solution (JEP 254)

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