Parameters

Parameters are variables that are defined in a method’s signature, allowing you to pass data into methods.

Basic Parameter Usage

public void greet(String name) {
  System.out.println("Hello, " + name + "!");
}

In this example, name is a parameter of type String.

Multiple Parameters

Methods can accept multiple parameters, separated by commas:

public int add(int num1, int num2) {
  return num1 + num2;
}

Parameter Types

Parameters can be of any valid Java type:

• Primitive types (int, boolean, double, etc.)
• Objects (String, ArrayList, custom classes)
• Arrays

public void processData(int id, String name, double[] values) {
  // Method body
}

Pass-by-Value

Java uses “pass-by-value” semantics for all parameters:

• For primitive types, a copy of the actual value is passed
• For objects, a copy of the reference is passed

public static void main(String[] args) {
  int x = 10;
  updateValue(x);
  System.out.println(x);  // Still outputs 10

  int[] arr = {1, 2, 3};
  updateArray(arr);
  System.out.println(arr[0]);  // Outputs 99
}

public static void updateValue(int value) {
  value = 20;  // Only changes the local copy
}

public static void updateArray(int[] array) {
  array[0] = 99;  // Modifies the actual array object
}

Variable-Length Parameters (Varargs)

Java supports variable-length parameter lists using ... syntax:

public int sum(int... numbers) {
  int total = 0;
  for (int num : numbers) {
    total += num;
  }
  return total;
}

// Can be called with any number of arguments
sum(1, 2);           // Returns 3
sum(1, 2, 3, 4, 5);  // Returns 15
sum();               // Returns 0

Varargs must be the last parameter in the method signature.

Final Parameters

You can declare parameters as final to prevent them from being modified within the method:

public void process(final int id) {
  // id = 100;  // This would cause a compilation error
  System.out.println("Processing ID: " + id);
}