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第四十一題：

Given:

public class KungFu {
    public static void main(String[] args) {
        Integer x = 400;
        Integer y = x;
        x++;
        StringBuilder sb1 = new StringBuilder("123");
        StringBuilder sb2 = sb1;
        sb1.append("5");
        System.out.println((x == y) + " " + (sb1 == sb2));
    }
}

What is the result?

A. true true
B. false true
C. true false
D. false false
E. Compilation fails.
F. An exception is thrown at runtime.

答案：Ｂ

執行結果：無

題目範圍：基本觀念 、WapperClass

解析：

Integer是int的WapperClass，雖然以物件的形式來表現，不過在做等於運算的時候要視為基本資料型態，以傳值的作法來做
一般物件的話當然做等於運算就是傳指標了

第四十二題：

class A {
    public String doit(int x, int y) {
        return "a";
    }

    public String doit(int... vals) {
        return "b";
    }
}

Given:

25. A a = new A();
26. System.out.println(a.doit(4, 5));

What is the result?

A. Line 26 prints "a" to System.out.
B. Line 26 prints "b" to System.out.
C. An exception is thrown at runtime.
D. Compilation of class A will fail due to an error in line 6.

答案：Ａ

執行結果：答案中

題目範圍：方法多載

解析：

這是方法多載比較特別的情況
當多重參數方法跟一般的多變數方法有類似的傳入值時，會優先採用多變數方法

第四十三題：

Given:

class Plant {
    private String name;

    public Plant(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

public class Tree extends Plant {
    public void growFruit() {
    }

    public void dropLeaves() {
    }
}

What statement is true?

A. The code will compile without changes.
B. The code will compile if public Tree(){Plant();} is added to the Tree class.
C. The code will compile if public Plant(){Tree();} is added to the Plant class.
D. The code will compile if public Plant(){this("fern");} is added to the Plant class.
E. The code will compile if public Plant(){Plant("fern");} is added to the Plant class.

答案：Ｄ

執行結果：無

題目範圍：物件觀念

解析：

繼承類別時，建構子的呼叫
父代如果只有需要參數的建構子，子代在建構子中，就必須寫出super() 來傳遞參數
否則就必須在父代增加一個無參數的建構子

第四十四題：

Given:

class Employee {
    String name;
    double baseSalary;

    public Employee(String name, double baseSalary) {
        this.name = name;
        this.baseSalary = baseSalary;
    }
}

public class SalesPerson extends Employee {
    double commission;

    public SalesPerson(String name, double baseSalary, double commission) {
        // insert code here
    }
}

Which two code fragments, inserted independently at line 12, will compile? (Choose two.)

A. super(name, baseSalary);

B. this.commission = commission;

C. super();

　this.commission = commission;

D. this.commission = commission;

　super();

E. super(name, baseSalary);

　this.commission = commission;

F. this.commission = commission;

　super(name, baseSalary);

G. super(name, baseSalary, commission);

答案：ＡＥ

執行結果：無

題目範圍：物件觀念

解析：

與四十三題觀念類似

第四十五題：

Given that:

Gadget has-a Sprocket and
Gadget has-a Spring and
Gadget is-a Widget and
Widget has-a Sprocket
Which two code fragments represent these relationships?
(Choose two.)

A. class Widget{Sprocket s;}
　class Gadget extends Widget{Spring s;}

B. class Widget{}
　class Gadget extends Widget{Spring s1; Sprocket s2;}

C. class Widget{Sprocket s1; Spring s2;}

　class Gadget extends Widget{}

D. class Gadget{Spring s;}

　class Widget extends Gadget{Sprocket s;}

E. class Gadget{}

　class Widget extends Gadget{Sprocket s1; Spring s2;}

F. class Gadget{Spring s1; Sprocket s2;}

　class Widget extends Gadget{}

答案：ＡＣ

執行結果：無

題目範圍：物件觀念

解析：

英文解釋：Gadget 機件，Widget 部件，Sprocket 鍊條，Spring 彈簧

Ａ完全符合題目

Ｂ的Widget 沒有容物，直到Gadget繼承了之後才加入，因此不正確

Ｃ的Widget 直接加入了兩個內容物，然後Gadget 繼承之後也會有父代的內容物，正確。題目沒有規定Widget 不能有其他的內容物

ＤＥＦ的繼承關係反了，也就沒甚麼好說的