Given the following class definition:
class A{
protected int i; A(int i){ this.i=i;
} }
which of the following would be a valid inner class for this class? Select all valid answers:
A. class B{ }
B. class B extends A{ }
C. class B extends A{
B(){System.out.println(“i=”+i);} }
D. class B{
class A{} }
E. class A{} 解答：A
点评：此题考查内部类及关键字“super”的用法。内部类不能与外部类同名。另外，当Ｂ继承Ａ时，Ａ中的构造函数是带参数的，Ｂ中缺省构造函数的函数体为空；而ＪＡＶＡ编译器会为空构造函数体自动添加语句“super();”调用父类构造函数，更进一步是调用父类的参数为空的构造函数。而父类中没有参数为空的构造函数。
例题22：
Which modifier should be applied to a method for the lock of object this to be obtained prior to excution any of the method body?
A. synchronized
B. abstract
C. final
D. static
E. public 解答：A
点评：此关键字可以在两个线程同时试图访问某一数据时避免数据毁损。
例题23：
The following code is entire contents of a file called Example.java,causes precisely one error during compilation:
1) class SubClass extends BaseClass{ 2) }
3) class BaseClass(){ 4) String str;
5) public BaseClass(){
6) System.out.println(“ok”);} 7) public BaseClass(String s){ 8) str=s;}}
9) public class Example{ 10) public void method(){
11) SubClass s=new SubClass(“hello”);
12) BaseClass b=new BaseClass(“world”); 13) } 14) }
Which line would be cause the error?
A. 9 B. 10 C. 11 D.12 解答：C
点评：当一个类中未显式定义构造函数时，缺省的构造函数是以类名为函数名，参数为空，函数体为空。虽然父类中的某一构造函数有字符串参数s，但是子类继承父类时并不继承构造函数，所以它只能使用缺省构造函数。故在第11行出错。 例题24：
Which statement is correctly declare a variable a which is suitable for refering to an array of 50 string empty object?
A. String [] a
B. String a[]
C. char a[][]
D. String a[50]
F. Object a[50] 解答：A,B
点评：注意，题中问的是如何正确声明一个一维数组，并非实例化或者初始化数组。
例题25：
Give the following java source fragement: //point x
public class Interesting{ //do something }
Which statement is correctly Java syntax at point x?
A. import java.awt.*;
B.package mypackage
C. static int PI=3.14
D. public class MyClass{//do other thing…} E. class MyClass{//do something…} 解答：A,E
点评：X处可以是一个输入，包的定义，类的定义。由于常量或变量的声明只能在类中或方法中，故不能选择C；由于在一个文件中只能有一个public类，故不能选择D。
例题26：
Give this class outline: class Example{ private int x;
//rest of class body… }
Assuming that x invoked by the code java Example, which statement can made x be directly accessible in main() method of Example.java?
A. Change private int x to public int x
B. change private int x to static int x
C. Change private int x to protected int x
D. change private int x to final int x 解答：B
点评：静态方法除了自己的参数外只能直接访问静态成员。访问非静态成员，必须先实例化本类的一个实例，再用实例名点取。
例题27：
the piece of preliminary analsis work describes a class that will be used frequently in many unrelated parts of a project
“The polygon object is a drawable, A polygon has vertex information stored in a vector, a color, length and width.”
Which Data type would be used?
A. Vector
B. int
C. String
D. Color
E. Date
解答：A,B,D
点评：polygon的顶点信息存放在Vector类型的对象内部，color定义为Color，length和width定义为int。
注意，这是考试中常见的题型。
例题28：
A class design requires that a member variable should be accessible only by same package, which modifer word should be used?
A. protected
B. public
C. no modifer
D. private
解答：C
点评：此题考点是高级访问控制。请考生查阅高级访问控制说明表格。
例题29：
Which declares for native method in a java class corrected?
A. public native void method(){}
B. public native void method();
C. public native method();
D. public void method(){native;}
E. public void native method(); 解答：B
点评：native关键字指明是对本地方法的调用，在JAVA中是只能访问但不能写的方法，它的位置在访问权限修饰语的后面及返回值的前面。
例题30：
Which modifer should be applied to a declaration of a class member variable for the value of variable to remain constant after the creation of the object? 解答：final
点评：定义常量的方法是在变量定义前加final关键字。
例题31：
Which is the main() method return of a application?
A. String
B. byte
C. char
D. void
解答：D
点评：main()方法没有返回值，所以必须用void修饰。main()方法的返回值不能任意修