例题1：
Choose the three valid identifiers from those listed below.
A. IDoLikeTheLongNameClass
B. $byte
C. const
D. _ok
E. 3_case
解答：A, B, D
点评：Java中的标示符必须是字母、美元符($)或下划线(_)开头。关键字与保留字不能作为标示符。选项C中的const是Java的保留字，所以不能作标示符。选项E中的3_case以数字开头，违反了Java的规则。
例题2：
How can you force garbage collection of an object?
A. Garbage collection cannot be forced
B. Call System.gc().
C. Call System.gc(), passing in a reference to the object to be garbage
collected.
D. Call Runtime.gc().
E. Set all references to the object to new values（null, for example）.
解答：A
点评：在Java中垃圾收集是不能被强迫立即执行的。调用System.gc()或Runtime.gc()静态方法不能保证垃圾收集器的立即执行，因为，也许存在着更高优先级的线程。所以选项B、D不正确。选项C的错误在于，System.gc()方法是不接受参数的。选项E中的方法可以使对象在下次垃圾收集器运行时被收集。
例题3：
Consider the following class:
1. class Test(int i) {
2. void test(int i) {
3. System.out.println(“I am an int.”);
4. }
5. void test(String s) {
6. System.out.println(“I am a string.”);
7. }
8.
9. public static void main(String args[]) {
10. Test t=new Test();
11. char ch=“y”;
12. t.test(ch);
13. }
14. }
Which of the statements below is true?(Choose one.)
A. Line 5 will not compile, because void methods cannot be overridden.
B. Line 12 will not compile, because there is no version of test() that
rakes a char argument.
C. The code will compile but will throw an exception at line 12.
D. The code will compile and produce the following output: I am an int.
E. The code will compile and produce the following output: I am a
String.
解答：D
点评：在第12行，16位长的char型变量ch在编译时会自动转化为一个32位长的int型，并在运行时传给void test(int i)方法。
例题4：
Which of the following lines of code will compile without error？
A. int i=0;
if (i) {
System.out.println(“
Hi”);
}
B.
boolean b=true;
boolean b2=true;
if(b==b2) {
System.out.println(“So true”);
}
C.
int i=1;
int j=2;
if(i==1|| j==2)
System.out.println(“OK”);
D.
int i=1;
int j=2;
if (i==1 &| j==2)
System.out.println(“OK”);
解答：B, C
点评：选项A错，因为if语句后需要一个boolean类型的表达式。逻辑操作有^、&、| 和
&&、||,但是“&|”是非法的，所以选项D不正确. |
