java when should i make a new class code example

Example 1: classes in java

// this might help you understand how classes work
public class MathTest {

    public static void main(String[] args) {

        class MathAdd {

            int num1;
            int num2;

            public int addNumbers() {

                int addThemUp = num1 + num2;
                return addThemUp;
            }
        }

        MathAdd addition = new MathAdd(); // create a new instance of the class

        // you can access variables from the class 
        addition.num1 = 10; 
        addition.num2 = 20;

        // and use the method from the class to add them up
        System.out.println(addition.addNumbers());

    }
}

Example 2: java class

//	Example : TestClass (Can be predefined or user-defined)
public class TestClass {
  // properties
  private int id = 111;
  
  // constructor
  public TestClass(){
    super();
  }
  
  // method
  public void test(){
    // some code here
  }
}