In Java, variables are only accessible inside the region 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:

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 blocks of code are only accessible by the code between the curly braces, which follows the line in which the variable was declared:

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

  }
}