Given:
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1 2 3 4 5 6 7 8 9 10 11 12 |
public abstract class Shape { private int x; private int y; public abstract void draw(); public void setAnchor(int x, int y) { this.x = x; this.x = y; } } |
Which two classes use the shape class correctly?
A.
|
1 2 3 |
public class Circle implements Shape{ private int radius; } |
B.
|
1 2 3 |
public abstract class Circle extends Shape{ private int radius; } |
C.
|
1 2 3 4 |
public class Circle extends Shape{ private int radius; public void draw(); } |
D.
|
1 2 3 4 |
public abstract class Circle implements Shape{ private int radius; public void draw(); } |
E.
|
1 2 3 4 |
public class Circle extends Shape{ private int radius; public void draw() { /* code here */ } } |
F.
|
1 2 3 4 |
public abstract class Circle implements Shape{ private int radius; public void draw() { /* code here */ } } |
題解
抽象類別內允許沒有實作的抽象方法。由於抽象類別也是類別，因此無法使用實作介面(interface)的「implements」關鍵字來實作，所以選項A、D、F都是錯誤的。另外，抽象類別的抽象方法必須被繼承該抽象類別的非抽象類別來實作，因此選項C也是錯誤的。
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