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Syllabus / Java / Phase 2: Control Flow & Data (Days 6–10)
Intermediate

Method Overloading and Variable Scope

📂 Phase 2: Control Flow & Data (Days 6–10) · Java

Method overloading lets you define multiple methods with the same name but different parameter lists — Java decides which version to call based on the arguments you pass.

Method Overloading Example

public static int add(int a, int b) {
    return a + b;
}

public static double add(double a, double b) {
    return a + b;
}

public static int add(int a, int b, int c) {
    return a + b + c;
}

public static void main(String[] args) {
    System.out.println(add(2, 3));        // calls version 1 → 5
    System.out.println(add(2.5, 3.5));     // calls version 2 → 6.0
    System.out.println(add(1, 2, 3));      // calls version 3 → 6
}

Rules for Valid Overloading

  • Methods must differ in the number of parameters, OR
  • Methods must differ in the type of parameters, OR
  • Methods must differ in the order of parameter types
Changing only the return type is NOT enough to overload a method — int add(int a, int b) and double add(int a, int b) with identical parameters will not compile.

Variable Scope

Scope determines where in your code a variable can be accessed. Java has three main scope levels:

ScopeWhere DeclaredAccessible From
LocalInside a method or blockOnly within that method/block
InstanceInside a class, outside any methodAny non-static method in that object
Class (static)Inside a class with the static keywordShared across all objects of the class

Local Scope Example

public static void method1() {
    int x = 10; // local to method1
    System.out.println(x);
}

public static void method2() {
    System.out.println(x); // ERROR — x doesn't exist here
}

Block Scope Inside Loops

for (int i = 0; i < 5; i++) {
    int square = i * i; // square only exists inside this loop body
}
// System.out.println(square); // ERROR — square is out of scope here
Interview tip: A favorite trick question is asking what happens if you declare a local variable with the same name as an instance variable — the local variable "shadows" the instance variable within that method, and you'd need this.variableName to access the instance version.