Java Scope

Java Scope

In Java, variables are only accessible inside the region where they are created. This is called scope.

Method Scope

Variables declared directly inside a method are available anywhere in the method following the line of code in which they were declared:

Example

public class Main {
  public static void main(String[] args) {

    // Code here CANNOT use x

    int x = 100;

    // Code here CAN use x
    System.out.println(x);
  }
}

Block Scope

A block of code refers to all of the code between curly braces { }.

Variables declared inside a block of code are only accessible by the code between the curly braces, and only after the line in which the variable was declared:

Example

public class Main {
  public static void main(String[] args) {

    // Code here CANNOT use x

    { // This is a block

      // Code here CANNOT use x

      int x = 100;

      // Code here CAN use x
      System.out.println(x);

    } // The block ends here

    // Code here CANNOT use x

  }
}

Note: A block of code can stand alone, or be part of an if, while, or for statement. In a for loop, the variable declared in the loop header (like int i = 0) only exists inside the loop.

Loop Scope

Variables declared inside a for loop only exist inside the loop:

Example

public class Main {
  public static void main(String[] args) {

    for (int i = 0; i < 5; i++) {
      System.out.println(i); // i is accessible here
    }

    // i is NOT accessible here
  }
}

• The for loop has its own block ({ ... }).
• The variable i declared in the loop header (int i = 0) is only accessible inside that loop block.
• Once the loop ends, i is destroyed, so you can't use it outside.

Why this matters

Loop variables are not available outside the loop.

You can safely reuse the same variable name (i, j, etc.) in different loops in the same method:

Example

public class Main {
  public static void main(String[] args) {

    for (int i = 0; i < 3; i++) {
      System.out.println("Loop 1: " + i);
    }

    for (int i = 0; i < 2; i++) {
      System.out.println("Loop 2: " + i);
    }
  }
}