JAVA认证历年真题：SCJP考试真题和解析
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。
Question No: 1 Given:
1. public class test (
2. public static void main (String args) { 3. int i = 0xFFFFFFF1; 4. int j = ~i; 5. 6. } 7. )
What is the decimal value of j at line 5? A. 0 B. 1 C. 14 D. –15
E. An error at line 3 causes compilation to fail. F. An error at line 4 causes compilation to fail. Answer: D
Question No: 2 Given:
Integer i = new Integer (42); Long 1 = new Long (42);
Double d = new Double (42.0);
Which two expressions evaluate to True? (Choose Two) A. (i ==1) B. (i == d) C. (d == 1) D. (i.equals (d)) E. (d.equals (i)) F. (i.equals (42)) Answer: D, E Question No: 3 Exhibit :
1. public class test ( 2. private static int j = 0; 3.
4. private static boolean methodB(int k) ( 5. j += k; 6. return true; 6. ) 7.
8. public static void methodA(int i) { 9. boolean b:
10. b = i < 10 | methodB (4); 11. b = i < 10 || methodB (8); 12. ) 13.
14. public static void main (String args } ( 15. methodA (0);
16. system.out.printIn(j); 17. ) 18. )
What is the result?
A. The program prints “0” B. The program prints “4” C. The program prints “8” D. The program prints “12” E. The code does not complete. Answer: B Question No: 4 Given
1. Public class test (
2. Public static void main (String args) ( 3. System.out.printIn (6 ^ 3); 4. ) 5. )
What is the output? Answer: 5 Question No: 5 Given:
1. public class Foo {
2. public static void main (String args) { 3. StringBuffer a = new StringBuffer (“A”); 4. StringBuffer b = new StringBuffer (“B”); 5. operate (a,b);
6. system.out.printIn{a + “,” +b}; 7. )
8. static void operate (StringBuffer x, StringBuffer y) { 9. x.append {y}; 10. y = x; 11. ) 12. }
What is the result?
A. The code compiles and prints “A,B”. B. The code compiles and prints “A,A”.
C. The code compiles and prints “B,B”. D. The code compiles and prints “AB,B”. E. The code compiles and prints “AB,AB”.
F. The code does not compile because “+” cannot be overloaded for StringBuffer. Answer: D ||| Question No: 6 Exhibit:
1. Public class test (
2. Public static void stringReplace (String text) ( 3. Text = text.replace (?j? , ?i?); 4. ) 5.
6. public static void bufferReplace (StringBuffer text) ( 7. text = text.append (“C”) 8. ) 9.
10. public static void main (String args} ( 11. String textString = new String (“java”);
12. StringBuffer text BufferString = new StringBuffer (“java”); 13.
14. stringReplace (textString); 15. BufferReplace (textBuffer); 16.
17. System.out.printIn (textString + textBuffer); 18. } 19. )
What is the output? Answer: javajavaC Question No: 7 Exhibit:
1. public class test {
2. public static void add3 (Integer i) } 3. int val = i.intValue ( ); 4. val += 3;
5. i = new Integer (val); 6. } 7.
8. public static void main (String args [ ] ) { 9. Integer i = new Integer (0); 10. add3 (i);
11. system.out.printIn (i.intValue ( ) ); 12. } 13. )
What is the result?