what does declaring a variable mean java code example

Example: Variables in java

// instance variable in java example
public class InstanceVariableDemo
{
   // instance variable declared inside the class and outside the method
   int c;
   public void subtract()
   {
      int x = 100;
      int y = 50;
      c = x - y;
      System.out.println("Subtraction: " + c);
   }
   public void multiply()
   {
      int m = 10;
      int n = 5;
      c = m * n;
      System.out.println("Multiplication: " + c);
   }
   public static void main(String[] args)
   {
      InstanceVariableDemo obj = new InstanceVariableDemo();
      obj.subtract();
      obj.multiply();
   }
}