练习题Quiz

Section 1

基于下面的代码

1 2 3 4 5 6 7 8 9 
public class Cla {    public void f1() {        System.out.println("cla f1")    }     public void f2() {        System.out.println("cla f2")    }}

1 2 3 4 5 
public class Dla extends Cla {    public void f3() {        System.out.println("dla f3")    }}

1 2 3 4 5 6 7 8 
public class Ela extends Dla {    public void f1() {        System.out.println("dla f1")    }    public void f4() {        System.out.println("ela f4")    }}

1 2 3 4 5 6 7 8 
public class Fla extends Cla {    public void f1() {        System.out.println("fla f1")    }    public void f5() {        System.out.println("fla f5")    }}

分析每个练习中的 被标记为 check 的那行代码

1. 编译时是否会报错

2. 如果1 不会报错，那么，运行时是否会报错

3. 如果1 2 都没错，如果 有输出代码，请写出输出结果

Exercise 1

方法覆盖对调用的影响

Case 1

Cla la = new Cla();
la.f1(); // check

Case 2

Dla la = new Dla();
la.f1(); // check

Case 3

Ela la = new Ela();
la.f1(); // check

Exercise 2

左右类型匹配

Case 1

Cla la = new Cla(); // check

Case 2

Dla la = new Dla(); // check

Case 3

Cla la = new Dla(); // check

Case 4

Dla la = new Cla(); // check

Exercise 3

权限对调用的影响

Case 1

Cla la = new Cla(); 
la.f1();    // check
la.f3();    // check

Case 2

Dla la = new Dla();
la.f1();    // check
la.f3();    // check

Case 3

Cla la = new Dla();
la.f1();    // check
la.f3();    // check

Exercise 4

转型规则

Case 1

Cla cla = new Dla();
Dla la = (Dla)la; // check;

Case 2

Cla cla = new Dla();
Ela la = (Ela)la; // check;

Case 3

Cla cla = new Dla();
Fla la = (Fla)la; // check;

Exercise 5

传参规则

Case 1

public class Driver {
    public void run() {
        func(new Cla()) // check
    }
    public void func(Cla la) {
        ...
    }
}

Case 2

public class Driver {
    public void run() {
        func(new Dla()) // check
    }
    public void func(Dla la) {
        ...
    }
}

Case 3

public class Driver {
    public void run() {
        func(new Cla()) // check
    }
    public void func(Dla la) {
        ...
    }
}

Case 4

public class Driver {
    public void run() {
        func(new Dla()) // check
    }
    public void func(Cla la) {
        ...
    }
}

Exercise 5

返回规则

Case 1

public class Driver {
    public void run() {
        func()
    }
    public Cla func() {
        return new Cla(); // check
    }
}

Case 2

public class Driver {
    public void run() {
        func()
    }
    public Dla func() {
        return new Dla(); // check
    }
}

Case 3

public class Driver {
    public void run() {
        func()
    }
    public Cla func() {
        return new Dla(); // check
    }
}

Case 4

public class Driver {
    public void run() {
        func()
    }
    public Dla func() {
        return new Cla(); // check
    }
}

Exercise 5

返回接收

Case 1

public class Driver {
    public void run() {
        Cla la = func(); // check
    }
    public Cla func() {
        return new Cla(); 
    }
}

Case 2

public class Driver {
    public void run() {
        Dla la = func(); // check
    }
    public Dla func() {
        return new Dla(); 
    }
}

Case 3

public class Driver {
    public void run() {
        Cla la = func(); // check
    }
    public Dla func() {
        return new Dla(); 
    }
}

Case 4

public class Driver {
    public void run() {
        Dla la = func(); // check
    }
    public Cla func() {
        return new Cla();
    }
}

Exercise 6

isClass

Case 1

Cla la = new Cla();
System.out.println(la.getClass() == Cla.class); // check

Case 2

Dla la = new Dla();
System.out.println(la.getClass() == Cla.class); // check 

Case 3

Cla la = new Dla();
System.out.println(la.getClass() == Cla.class); // check 

Case 3

Cla la = new Dla();
System.out.println(la.getClass() == Dla.class); // check