JAVA认证:SCJP考试真题和剖析

会计考友

例题1：
( e- |$ v/ q/ s/ a& G9 T' `Choose the three valid identifiers from those listed below.
A. IDoLikeTheLongNameClass
  w+ s$ F& u$ \/ t+ h. r* N+ {, UB. $byte
C. const
1 r8 i0 [6 g7 Y3 m  v% HD. _ok
: v& w9 ?$ n% L( wE. 3_case
解答：A， B， D
点评：Java中的标示符必须是字母、美元符($)或下划线(_)开头。关键字与保留字不能作为标示符。选项C中的const是Java的保留字，所以不能作标示符。选项E中的3_case以数字开头，违反了Java的规则。
0 W* |: @; T9 I( ~$ v+ u例题2：
$ v- j( B/ f! f+ a# y4 NHow 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.
% T/ y" s1 ^9 u, F4 UD. Call Runtime.gc().
E. Set all references to the object to new values（null， for example）.
- s2 p' E6 ^$ M$ n6 }: f' ^解答：A
) A, H# O7 i/ w5 F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. }
. M, J4 h7 U0 h. X- }8.
8 p' {" t: D6 `$ ^! I2 @/ }6 s* B9. public static void main(String args) {
10. Test t=new Test();
11. char ch=“y”;
( v2 b/ ^3 `, N+ P+ O12. t.test(ch);
13. }
" h1 T0 w6 R& S% t7 v1 z' R& k14. }
Which of the statements below is true?(Choose one.)
& D; f: d, _: z0 g9 ?A. Line 5 will not compile， because void methods cannot be overridden.
: |% N# j- }& L( ?' IB. 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.
0 m3 M' K$ s4 d! M; n& mD. 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.
6 B0 b: w9 U0 O7 w8 v# E+ L2 M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。