Java Programming Language Cheat Sheet

Java is a strongly-typed, object-oriented, and platform-independent programming language. This cheat sheet covers core syntax and standard library usage commonly used in Java development.

Basics

Primitive Types

• Integers: byte (8b), short (16b), int (32b), long (64b)
• Floating point: float (32b), double (64b)
• Character: char (16b Unicode)
• Boolean: boolean (true/false)

Key Keywords

Java cheat sheet, Java syntax, Collections framework, Multi-threading, Programming manual

OOP

// Class definition
public class Person extends BaseEntity implements Walkable {
    private String name; // Encapsulation
    
    public Person(String name) {
        this.name = name;
    }
    
    @Override
    public void walk() {
        System.out.println(name + " is walking");
    }
}

Collections Framework

// Common operations

List<String> list = new ArrayList<>();
list.add("Apple");
list.get(0);

Map<String, Integer> map = new HashMap<>();
map.put("Key", 100);
map.get("Key");

Lambda & Stream (Java 8+)

Functional Interfaces

• Predicate<T>: Returns boolean
• Function<T, R>: Takes T, returns R
• Consumer<T>: Takes T, no return
• Supplier<T>: No input, returns T

// Common stream operations

List<String> result = names.stream()
    .filter(s -> s.startsWith("A"))    
    .map(String::toUpperCase)          
    .sorted()                          
    .collect(Collectors.toList());      

Exception Handling

try {
    // Code that might fail
} catch (IOException e) {
    // Handle specific exception
} finally {
    // Always executes
}

// // Try-with-resources (auto-close)
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
    return br.readLine();
}

Common Commands (CLI)

• javac Main.java : Compile
• java Main : Run
• jar -cvf app.jar *.class : Package
• javadoc -d doc Main.java : Generate documentation