SCJP題庫第050題

1. public abstract class Shape{

2.   private int x;

3.   private int y;

4.   public abstract void draw();

5.   public void setAnchor(int x, int y){

6.     this.x = x;

7.     this.y = y;

8.   }

9. }

Which two classes use the Shape class correctly? (Choose two.)

A.

public class Circle implements Shape{

  private in radius;

}

B.

public abstract class Circle extends Shape{

  private in radius;

}

C.

public class Circle extends Shape{

  private in radius;

  public void draw();

} 
D.

public abstract class Circle implements Shape{

  private in radius;

  public void draw();

}

E.

public class Circle extends Shape{

  private in radius;

  public void draw(){/* code here */}

}

F.

public abstract class Circle implements Shape{

  private in radius;

  public void draw(){/* code here */}

}

Ans:B  E

解說:

一個類別中若有抽象方法(沒有實作)，則類別必須為abstract，Circle繼承抽象類別Shape，若Circle不為抽象類別，必須對繼承自Shape的抽象方法補上實作
使用implements必須針對介面的類別。(A/D/F錯)