Debugging using terminal

import java.util.*;

public class AreaCalculator {

    public static void main(String[] args) {

      Scanner keyboard = new Scanner(System.in);

      System.out.println("Shape Area Calculator");

      while(true) {   //indicates an infinite loop, hence break is written at the end to exit the loop

        System.out.println();
        System.out.println("-=-=-=-=-=-=-=-=-=-");
        System.out.println();
        System.out.println("1) Triangle");
        System.out.println("2) Rectangle");
        System.out.println("3) Circle");
        System.out.println("4) Quit");
        System.out.println();

        System.out.print("Which shape: ");

      int shape = keyboard.nextInt();
      System.out.println();

        if (shape == 1) {
            area_triangle(5,6);   //arguments here act as 'default' -- not used here since each method ask user input
        } else if (shape == 2) {
            area_rectangle(4,5);
        } else if (shape == 3) {  //corrected to 3
            area_circle(4);
        } else if (shape == 4) {
            quit();
            break;
        }
      }
  }

  public static double area_triangle(int base, int height) {

        Scanner keyboard = new Scanner(System.in);

        System.out.print("Base: ");
        base = keyboard.nextInt();

        System.out.print("Height: ");
        height = keyboard.nextInt();

        System.out.println();

        int A = (base * height) * 1/2;  //corrected to 1/2

        System.out.println("The area is " + A + ".");

        return A;
    }

  public static int area_rectangle(int length, int width){

        Scanner keyboard = new Scanner(System.in);

        System.out.print("Length: ");
        length = keyboard.nextInt();

        System.out.print("Width: ");
        width = keyboard.nextInt();

        System.out.println();

        int A = length * width;

        System.out.println("The area is " + A + ".");

        return A;
    }

  public static double area_circle(int radius) {

        Scanner keyboard = new Scanner(System.in);

        System.out.print("Radius: ");
        radius = keyboard.nextInt();

        System.out.println();

        double A = Math.PI * radius * radius;

        System.out.println("The area is " + A + ".");

        return A;
    }

    public static String quit() {
        System.out.println("GoodBye");
        return null;
    }
}
/*
To test for syntax error using the compiler, type:
javac AreaCalculator.java

To test program for logic error, type:
java AreaCalculator
*/