Question

I’m trying out java and I seem to be running into some problems. The only problem I seem to be having is when I add an extension of the Stars class, the constructor seems to be called without me declaring one like Stars test = new Star();

Knight.java

import javax.swing.JOptionPane;

public class Knight extends Stars {
    private String name;
    private int health, battles, age, gold;

    public Knight() {
        name = JOptionPane.showInputDialog("What is the knight's name?");
        String message = String.format("How much health does %s have?", name);
        health = Integer.parseInt(JOptionPane.showInputDialog(message));
        message = String.format("How many battles has %s been in?", name);
        battles = Integer.parseInt(JOptionPane.showInputDialog(message));
        message = String.format("How old is %s?", name);
        age = Integer.parseInt(JOptionPane.showInputDialog(message));
        message = String.format("How much gold does %s have?", name);
        gold = Integer.parseInt(JOptionPane.showInputDialog(message));
    }

    public String getStats() {
        // String message = 
        return String.format("\nKnight Name: %s\nKnight Health: %d\nKnight Battles: %d\nKnight Age: %d\nKnight Gold: $%d\n\n", name, health, battles, age, gold);
    }

}

Stars.java
import javax.swing.JOptionPane;

public class Stars {
    private int rows, cols;
    private String skyScape = new String();

    public Stars() {
        rows = Integer.parseInt(JOptionPane.showInputDialog("How many rows of stars are there?"));
        cols = Integer.parseInt(JOptionPane.showInputDialog("How many columns of stars are there?"));
        for (int count = 0; count < rows; ++count) {
            if ((count % 2) == 1) {
                skyScape += " *";
            } else {
                skyScape += "*";
            }
            for (int colCount = 1; colCount < cols; ++colCount) {
                    skyScape += " *";
                    if (colCount == cols - 1) {
                        skyScape += "\n";
                    }
            }
        }
    }

    public int getRows() {
        return rows;
    }

    public int getCols() {
        return cols;
    }

    public String getSky() {
        return skyScape;
    }
}

Any help would be appreciated!

Answer 1

Java requires that every constructor (except Object’s) call some superclass constructor, to ensure that the data contained in the superclass is initialized. If you don’t call a superclass constructor explicitly, the compiler will insert an implicit call to the default (zero-argument) constructor of the superclass.