Javaでフィールドに代入して初期化するのとコンストラクタの中で初期化するのって微妙に違うことを表したかったんだけど、さほど納得感が出なかった・・・

Main.java

public class Main {
    public static void main(String... args) {
        SuperHoge superHoge_1 = new SuperHoge();
        System.out.println(superHoge_1.sum()); // => 2 (a:1, b:1)

        SuperHoge superHoge_2 = new SuperHoge(2);
        System.out.println(superHoge_2.sum()); // => 3 (a:1, b:2)

        SubHoge1 subHoge1_1 = new SubHoge1();
        System.out.println(subHoge1_1.sum()); // => 2 (a:1, b:1)

        SubHoge1 subHoge1_2 = new SubHoge1(2);
        System.out.println(subHoge1_2.sum()); // => 4 (a:1, b:3)

        SubHoge2 subHoge2_1 = new SubHoge2();
        System.out.println(subHoge2_1.sum()); // => 1 (a:0, b:1)

        SubHoge2 subHoge2_2 = new SubHoge2(2);
        System.out.println(subHoge2_2.sum()); // => 7 (a:0, b:7)
    }
}

SubHoge1.java

public class SubHoge1 extends SuperHoge {

    protected int a = 0; // これは使われない

    public SubHoge1() {
        super();
    }

    public SubHoge1(int value) {
        this();
        this.b += value;
    }
}

SubHoge2.java

public class SubHoge2 extends SuperHoge {

    {
        this.a = 0; // これはaを上書きできる
    }

    public SubHoge2() {
        super();
    }

    public SubHoge2(int value) {
        super(3 + value); // こういうのはコンストラクタならではかなと
        this.b += value;
    }
}

SuperHoge.java

public class SuperHoge {

    protected int a = 1;
    int b;

    protected SuperHoge() {
        this.b = 1;
    }

    protected SuperHoge(int value) {
        this.b = value;
    }

    public int sum() {
        return a + b;
    }
}