java - 失败“字段应该使用接口(interface)的实现实例初始化”吗？

    public class Player implements Comparable<Player> {

//Fields
private Name name;
private Rollable rollable;

//Constructors
public Player() {
    name = new Name();
    rollable = new Rollable();
}
public Player(Name name) {
    this.name = name;
    rollable = new Rollable();
}
public Player(Name name, Rollable rollable) {
    this.name = name;
    this.rollable = rollable;
}

您好，对于我放置rollable = new Rollable();的构造函数，我收到一条错误消息，指出它是Cannot instantiate the type rollable。
在下面，我添加了JUnit测试，还将添加Rollable类的代码

        @Test
public void testDefaultConstructor() {
    Player p = new Player();

    assertEquals("Name field should be initialised with a default Name object ", new Name(), p.

getName（））;
        assertTrue（“播放器的rollable字段应使用Rollable接口的实现实例初始化”，p.getRollable（）Rollable实例）；
            }

@Test
public void testCustomConstructor1arg() {
    Name n = new Name("Joe", "Bloggs");
    Player p = new Player(n);

    assertSame("Player's name field should be initialised with and      return the same object received by the constructor", n, p.getName());
    assertTrue("Player's rollable field should be initialised with an implementing instance of the Rollable interface", p.getRollable() instanceof Rollable);
}

现在下面是默认构造函数的JUnit测试，这也给我Players rollable field should be initialised with an implementing instance of the Rollable interface带来了失败，但是，我所有其他的JUnit测试都通过了。

        @Test
public void testDefaultConstructor() {
    Player p = new Player();

    assertEquals("Name field should be initialised with a default Name object ", new Name(), p.getName());
    assertTrue("Player's rollable field should be initialised with an implementing instance of the Rollable interface", p.getRollable() instanceof Rollable);
}

我的Rollable类的代码如下：

    public interface Rollable {

public void roll();

public int getScore();

}

我的可滚动代码的方法如下：

        //Methods
public Name getName() {
    return name;
}
public void setName(Name name) {
    this.name = name;
}
public Rollable getRollable() {
    return rollable;
}
public void rollDice() {
    rollable.roll();
}
public int getDiceScore() {
    return rollable.getScore();
}

感谢我为失败而苦苦挣扎的所有帮助。

最佳答案

您的getRollable()方法是：

public Rollable getRollable() {
    return rollable;
}

因此，例如，如果从构造函数调用它，则：

public Player() {
    name = new Name();
    rollable = getRollable();
}

然后将为rollable分配rollable的值，默认情况下为null。

这样，当您在测试中再次调用getRollable()时，您将获得分配给该字段的值-null-并且根据定义-null instanceof Rollable为false。

相反，您需要创建一个新的Rollable实例，例如：

rollable = new Rollable();

（不知道它是否可以直接实例化。您没有提供Rollable类的声明）。