Method Parameters

1// Basic parameters
2public void greet(String name) {          // 'name' is parameter
3    System.out.println("Hello, " + name);
4}
5
6greet("Alice");  // "Alice" is argument
7
8// Multiple parameters
9public int add(int a, int b) {
10    return a + b;
11}
12
13int result = add(5, 3);  // 5 and 3 are arguments
14
15// Parameters with same type
16public void printRange(int start, int end) {
17    for (int i = start; i <= end; i++) {
18        System.out.print(i + " ");
19    }
20}
21
22printRange(1, 5);  // 1 2 3 4 5

1// Pass by value - Primitives
2public static void changePrimitive(int x) {
3    x = 100;  // Only changes LOCAL copy!
4}
5
6int num = 5;
7changePrimitive(num);
8System.out.println(num);  // Still 5! (unchanged)
9
10// Pass by value - Objects (reference is copied)
11public static void modifyObject(StringBuilder sb) {
12    sb.append(" World");  // Modifies original object!
13}
14
15StringBuilder builder = new StringBuilder("Hello");
16modifyObject(builder);
17System.out.println(builder);  // "Hello World" (modified!)
18
19// Cannot reassign reference
20public static void tryReassign(StringBuilder sb) {
21    sb = new StringBuilder("New");  // Only changes LOCAL reference!
22}
23
24StringBuilder builder2 = new StringBuilder("Original");
25tryReassign(builder2);
26System.out.println(builder2);  // "Original" (unchanged!)

1// Different parameter types
2public class ParameterExamples {
3    
4    // Primitive parameters
5    public double calculateCircleArea(double radius) {
6        return Math.PI * radius * radius;
7    }
8    
9    // Object parameter
10    public void printPerson(Person person) {
11        System.out.println(person.getName());
12    }
13    
14    // Array parameter
15    public int sum(int[] numbers) {
16        int total = 0;
17        for (int n : numbers) {
18            total += n;
19        }
20        return total;
21    }
22    
23    // Varargs (variable arguments)
24    public int sumAll(int... numbers) {
25        int total = 0;
26        for (int n : numbers) {
27            total += n;
28        }
29        return total;
30    }
31}
32
33// Calling varargs
34sumAll(1, 2, 3);           // 6
35sumAll(1, 2, 3, 4, 5);     // 15
36sumAll();                   // 0

1// Final parameters
2public void process(final int value) {
3    // value = 10;  // ERROR! Cannot reassign final parameter
4    System.out.println(value);
5}
6
7// Helps prevent accidental modification
8
9// Default parameter values (NOT supported in Java!)
10// public void greet(String name = "Guest") {}  // NOT VALID!
11
12// Workaround: Method overloading
13public void greet() {
14    greet("Guest");  // Call with default
15}
16
17public void greet(String name) {
18    System.out.println("Hello, " + name);
19}
20
21// Or use Optional (Java 8+)
22public void greet(Optional<String> name) {
23    System.out.println("Hello, " + name.orElse("Guest"));
24}
25
26// Or builder pattern for many optional params
27User.builder()
28    .name("Alice")
29    .age(25)        // Optional
30    .build();