Java Syntax Quick Reference

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Primitive Types

Access Modifiers

Non-Access Modifiers

• static — belongs to class, not instance
• final — class: can't extend; method: can't override; variable: constant
• abstract — class: can't instantiate; method: no body, must override
• synchronized — thread-safe access
• transient — skip field during serialization
• volatile — always read from main memory

Class Structure

public class MyClass extends Parent implements Interface1, Interface2 {    // Fields (prefer private)    private int x;    // Constructor — same name as class, no return type    public MyClass(int x) { this.x = x; }    // Getter    public int getX() { return x; }    // Setter    public void setX(int x) { this.x = x; }    // Static method    public static void main(String[] args) { }    // Inner class    static class Helper { }}

Constructor Patterns

// Default constructor (Java provides if none defined)public MyClass() { }// Parameterized constructorpublic MyClass(int x) { this.x = x; }// Constructor chainingpublic MyClass()      { this(0); }public MyClass(int x) { this.x = x; }

Common Patterns

// For-each over array/Iterablefor (Type item : collection) { }// Scanner inputScanner sc = new Scanner(System.in);// String builderStringBuilder sb = new StringBuilder();sb.append("a").append("b");// try-with-resources (Java 7+)try (Scanner sc = new Scanner(new File("x.txt"))) { }// Enhanced switch (Java 14+)String result = switch (day) {    case 1 -> "Monday";    case 2 -> "Tuesday";    default -> "Unknown";};

Common Gotchas

• == compares references for objects, use .equals()
• Strings are immutable — + in loops creates many objects, use StringBuilder
• Integer caching: Integer.valueOf(127) == Integer.valueOf(127) is true, but 128 is false
• Switch needs break or fall-through happens
• Array index out of bounds is a runtime exception, not compile-time