1、计算机 Java认证-3 及答案解析(总分：100.00，做题时间：90 分钟)一、不定项选择题(总题数：44，分数：100.00)1.Concerning Java“s Garbage Collector (GC), which are true? (Choose all that apply.)（分数：1.50）A.If Object X has a reference to Object Y, then Object Y cannot be GCed.B.A Java program can request that the GC runs, but such a request doe
2、s NOT guarantee that the GC will actually run.C.If the GC decides to delete an object, and if finalize() has never been invoked for that object, it is guaranteed that the GC will invoke finalize() for that object before the object is deleted.D.Once the GC invokes finalize() on an object, it is guara
3、nteed that the GC will delete that object once finalize() has completed.E.When the GC runs, it decides whether to remove objects from the heap, the stack, or both.2.Given: 1. public class BackHanded 2. int state = 0; 3. BackHanded(int s) state = s; 4. public static void main(String. hi) 5. BackHande
4、d b1 = new BackHanded(1); 6. BackHanded b2 = new BackHanded(2); 7. System.out.println(b1.go(b1) + “ “ + b2.go(b2); 8. 9. int go(BackHanded b) 10. if(this.state = 2) 11. b.state = 5; 12. go(this); 13. 14. return +this.state; 15. What is the result?（分数：1.50）A.1 2B.1 3C.1 6D.1 7E.2 6F.2 7G.Compilation
5、fails.H.An exception is thrown at runtime.3.Given: 42. String s = “; 43. if(011 = 9) s += 4; 44. if(0x11 = 17) s += 5; 45. Integer I = 12345; 46. if(I.intValue() = Integer.valueOf(“12345“) s += 6; 47. System.out.println(s); What is the result?（分数：1.50）A.5B.45C.46D.56E.456F.Compilation fails.G.An exc
6、eption is thrown at runtime.4.Given: 3. class Sport 4. Sport play() System.out.print(“play “); return new Sport(); 5. Sport play(int x) System.out.print (“play x “); return new Sport(); 6. 7. class Baseball extends Sport 8. Baseball play() System.out.print(“baseball “); return new Baseball(); 9. Spo
7、rt play(int x) System.out.print(“sport “); return new Sport(); 10. 11. public static void main(String args) 12. new Baseball() .play(); 13. new Baseball() .play(7); 14. super.play (7); 15. new Sport().play(); 16. Sport s = new Baseball(); 17. s.play(); 18. What is the result?（分数：1.50）A.baseball spor
8、t sport play playB.baseball sport play x play sportC.baseball sport play x play baseballD.Compilation fails due to a single error.E.Compilation fails due to errors on more than one line.5.Given: 2. public class Self extends Thread 3. public static void main(String args) 4. try 5. Thread t = new Thre
9、ad(new Self(); 6. t.start(); 7. t.start(); 8. catch (Exception e) System.out.print(“e “); 9. 10. public void run() 11. for(int i = 0; i 2; i+) 12. System.out.print(Thread.currentThread() .getName() + “ “ ); 13. Which are true? (Choose all that apply.)（分数：1.50）A.Compilation fails.B.No output is produ
10、ced.C.The output could be Thread-1 Thread-1 eD.The output could be Thread-1 e Thread-1E.The output could be Thread-1 Thread-1 Thread-2 Thread-2F.The output could be Thread-1 Thread-2 Thread-1 Thread-2G.The output could be Thread-1 Thread-1 Thread-1 Thread-16.Given: 3. class Stereo void makeNoise() a
11、ssert true; 4. public class BoomBox2 extends Stereo 5. public static void main(String args) 6. new BoomBox2() .go(args); 7. 8. void go(String args) 9. if(args.length 0) makeNoise(); 10. if(args0 .equals(“x“) System.out.print(“x “); 11. if(args0 = “x“) System.out.println(“x2 “); 12. And (if the code
12、compiles), the invocation: java -ea Boombox2 x What is the result?（分数：1.50）AxB.xx2C.An Error is thrown at runtime.D.Compilation fails due to an error on line 3.E.Compilation fails due to an error on line 8.F.Compilation fails due to an error on line 9.7.Given: 2. import java.util.*; 3. public class
13、Olives 4. public static void main(String args) 5. SetInteger s = new TreeSetInteger(); 6. s.add(23); s.add(42); s.add(new Integer(5); 7. Iterator i = s.iterator(); 8. / while(System.out.print(i.next() 9. / for(Integer i2: i) System.out.print(i2); 10. / for(Integer i3: s) System.out.print(i3); 11. /
14、while(i.hasNext() System.out.print(i.get(); 12. / while(i.hasNext() System.out.print(i.next(); 13. If lines 8-12 are uncommented, independently, which are true? (Choose all that apply.)（分数：1.50）A.Line 8 will compile.B.Line 9 will compile.C.Line 10 will compile.D.Line 11 will compile.E.Line 12 will c
15、ompile.F.Of those that compile, the output will be 23425G.Of those that compile, the output will be 523428.Given the proper import statements and: 23. try 24. File file = new File(“myFile.txt“); 25. PrintWriter pw = new PrintWriter(file); 26. pw.println(“line 1“); 27. pw.close(); 28. PrintWriter pw2
16、 = new PrintWriter(“myFile.txt“); 29. pw2.println(“line 2“); 30. pw2.close(); 31. catch (IOException e) What is the result? (Choose all that apply.)（分数：1.50）A.No file is created.B.A file named “myFile.txt“ is created.C.Compilation fails due to an error on line 24.D.Compilation fails due to an error
17、on line 28.E.“myFile.txt“ contains only one line of data, “line 1“F.“myFile.txt“ contains only one line of data, “line 2“G.“myFile.txt“ contains two lines of data, “line 1“ then “line 2“9.Given this code in a method: 3. String s = “-“; 4. boolean b = false; 5. int x = 7, y = 8; 6. if(x 8) (b = true)
18、 s + “; 7. if(! (x 8) | +y 5) s += “|“; 8. if(+y 9 9. if(y % 8 1 | y / (x - 7) 1) s += “%“; 10. System.out.println(s); What is the result?（分数：1.50）A.-B.-|%C.-|%D.-| 5. protected int y = 3; 6. private static int m1 = 4; 7. protected static int m2 = 5; 8. public static void main(String args) 9. int x
19、= 6; int y = 7; 10. int m1 = 8; int m2 = 9; 11. new Limits().new Secret().go(); 12. 13. class Secret 14. void go() System.out.println(x + “ “ + y + “ “ + m1 + “ “ + m2); 15. What is the result?（分数：1.50）A.2 3 4 5B.2 7 4 9C.6 3 8 4D.6 7 8 9E.Compilation fails due to multiple errors.F.Compilation fails
20、 due only to an error on line 11.G.Compilation fails due only to an error on line 14.11.Given: 3. import java.io.*; 4. class ElectronicDevice ElectronicDevice() System.out.print(“ed “); 5. class Mp3player extends ElectronicDevice implements Serializable 6. Mp3player() System.out.print(“mp “); 7. 8.
21、class MiniPlayer extends Mp3player 9. MiniPlayer() System.out.print(“mini “); 10. public static void main(String args) 11. MiniPlayer m = new MiniPlayer(); 12. try 13. FileOutputStream fos = new FileOutputStream(“dev.txt“); 14. ObjectOutputStream os = new ObjectOutputStream(fos); 15. os.writeObject(
22、m); os.close(); 16. FileInputStream fis = new FileInputStream(“dev.txt“); 17. ObjectInputStream is = new ObjectInputStream(fis); 18. MiniPlayer m2 = (MiniPlayer) is.readObject(); is.close(); 19. catch (Exception x) System.out.print(“x “); 20. What is the result?（分数：2.50）A.ed mp miniB.ed mp mini edC.
23、ed mp mini ed miniD.ed mp mini ed mp miniE.Compilation fails.F.“ed mp mini“, followed by an exception.12.Given: 2. abstract interface Pixie 3. abstract void sprinkle(); 4. static int dust = 3; 5. 6. abstract class TinkerBell implements Pixie 7. String fly() return “flying “; 8. 9. public class ForRe
24、al extends TinkerBell 10. public static void main(String args) 11. new ForReal() .sprinkle(); 12. 13. public void sprinkle() System.out.println(fly() + “ “ + dust); 14. What is the result? (Choose all that apply.)（分数：2.50）A.flying 3B.Compilation fails because TinkerBell doesn“t properly implement Pi
25、xie.C.Compilation fails because ForReal doesn“t properly extend TinkerBell.D.Compilation fails because Pixie is not a legal interface.E.Compilation fails because ForReal doesn“t properly implement Pixie.F.Compilation fails because TinkerBell is not a legal abstract class.13.Given: 2. public class Er
26、rrrr 3. static String a = null; 4. static String s = “; 5. public static void main(String args) 6. try 7. a = args0; 8. System.out.print(a); 9. s += “t1 “; 10. 11. catch (RuntimeException re) s += “c1 “; 12. finally s += “f1 “; 13. System.out.println(“ “ + s); 14. And two command-line invocations: j
27、ava Errrrr java Errrrr x What is the result?（分数：2.50）A.First: f1, then: x t1B.First: f1, then: x t1 f1C.First: c1, then: x t1D.First: c1, then: x t1 f1E.First: c1 f1, then: x t1F.First: c1 f1, then: x t1 f1G.Compilation fails.14.Given: 51. String s = “4.5x4.a.3“; 52. String tokens = s.split(“/s“); 5
28、3. for(String o: tokens) 54. System.out.print (o + “ “); 55. 56. System.out.print(“ “); 57. tokens = s.split(“/“); 58. for(String o: tokens) 59. System.out.print(o + “ “); What is the result?（分数：2.50）A.4x4B.4x4.C.4x4 3D.45x4 a 3 4x4E.4.5x4.a.3 4x4F.4.5x4.a.3 4x4.15.Given: 2. abstract class Too1 3. i
29、nt SKU; 4. abstract void getSKU(); 5. 6. public class Hammer 7. / insert code here 8. Which line(s), inserted independently at line 7, will compile? (Choose all that apply.)（分数：2.50）A.void getSKU() ; B.private void getSKU() ; C.protected void getSKU() ; D.public void getSKU() ; 16.Given: 3. public c
30、lass Stubborn implements Runnable 4. static Thread t1; 5. static int x = 5; 6. public void run() 7. if(Thread.currentThread() .getId() = t1.getId() shove(); 8. else push(); 9. 10. static synchronized void push() shove(); 11. static void shove() 12. synchronized (Stubborn. class) 13. System.out.print
31、(x- + “ “); 14. try Thread.sleep(2000); catch (Exception e) ; 15. if(x 0) push(); 16. 17. public static void main(String args) 18. t1 = new Thread(new Stubborn(); 19. t1.start(); 20. new Thread(new Stubborn() .start(); 21. Which are true? (Choose all that apply.)（分数：2.50）A.Compilation fails.B.The ou
32、tput is 5 4 3 2 1C.The output is 5 4 3 2 1 0D.The program could deadlock.E.The output could be 5, followed by deadlock.F.If the sleep() invocation was removed, the chance of deadlock would decrease.G.As it stands, the program can“t deadlock, but if shove() was changed to synchronized, then the progr
33、am could deadlock.17.Given: 2. class Super 3. static String os = “; 4. void doStuff() os += “super “; 5. 6. public class PolyTest extends Super 7. public static void main(String args) new PolyTest().go(); 8. void go() 9. Super s = new PolyTest(); 10. PolyTest p = (PolyTest)s; 11. p.doStuff(); 12. s.
34、doStuff(); 13. p.doPoly(); 14. s.doPoly(); 15. System.out.println(os); 16. 17. void doStuff() os += “over “; 18. void doPoly() os += “poly “; 19. What is the result?（分数：2.50）A.Compilation fails.B.over over poly polyC.over super poly polyD.super super poly polyE.An exception is thrown at runtime.18.G
35、iven two files: 1. package com. wickedlysmart; 2. import com.wickedlysmart2.*; 3. public class Launcher 4. public static void main(String args) 5. Utils u = new Utils(); 6. u.do1(); 7. u.do2(); 8. u.do3(); 9. and the correctly compiled and located: 1. package com.wickedlysmart2; 2. class Utils 3. vo
36、id do1() System.out.print(“dol “); 4. protected void do2() System.out.print(“do2 “); 5. public void do3() System.out.print(“do3 “); 6. What is the result for Launcher? (Choose all that apply.)（分数：2.50）A.do1 do2 do3B.“do1 “, followed by an exceptionC.Compilation fails due to an error on line 5 of Lau
37、ncher.D.Compilation fails due to an error on line 6 of Launcher.E.Compilation fails due to an error on line 7 of Launcher.F.Compilation fails due to an error on line 8 of Launcher.19.Given: 2. public class Wacky 3. public static void main(String args) 4. int x = 5; 5. int y = (x 6) ? 7 : 8; 6. Syste
38、m.out.print(y + “ “); 7. boolean b = (x 6) ? false : true; 8. System. out .println (b + “ “); 9. assert(x 6) : “bob“; 10. assert( (x 6) ? false : true) ) : “fred“; 11. And, if the code compiles, the invocation: java -ea Wacky Which will be contained in the output? (Choose all that apply.)（分数：2.50）A.
39、7B.8C.bobD.fredE.trueF.falseG.Compilation fails.20.Given: 3. class MotorVehicle 4. protected int doStuff(int x) return x * 2; 5. 6. class Bicycle 7. void go(MotorVehicle m) 8. System.out.print(m. doStuff (21) + “ “); 9. 10. public class Beemer extends MotorVehicle 11. public static void main(String
40、args) 12. System.out.print(new Beemer().doStuff(11) + “ “); 13. new Bicycle().go(new Beemer(); 14. new Bicycle() .go(new MotorVehicle(); 15. 16. int doStuff(int x) return x * 3; 17. What is the result? (Choose all that apply.)（分数：2.50）A.22 42 42B.22 63 63C.33 42 42D.33 63 42E.Compilation fails.F.An
41、exception is thrown at runtime.21.Which are true? (Choose all that apply.)（分数：2.50）A.A single JAR file can contain only files from a single package.B.A JAR file can be used only on the machine on which it was created.C.When javac is using files within a JAR file, it will unJAR the file during compil
42、ation.D.The Java SDK installation directory tree on a Java developer“s computer usually includes a subdirectory tree named jre/lib/ext.E.A JAR file is structured so that all the files and directories that you“ve “JARed“ will be subdirectory(ies) of the META-INF directory.F.When javac is invoked with
43、 a classpath option, and you need to find files in a JAR file, the name of the JAR file must be included at the end of the path.22.Given the proper import(s), and given: 13. class NameCompare implements ComparatorStuff 14. public int compare(Stuff a, Stuff b) 15. return pareTo(a.name); 16. 18. class
44、 ValueCompare implements ComparatorStuff 19. public int compare(Stuff a, Stuff b) 20. return (a.value - b.value); 21. Which are true? (Choose all that apply.)（分数：2.50）A.This code does not compile.B.This code allows you to use instances of Stuff as keys in Maps.C.These two classes properly implement
45、the Comparator interface.D.NameCompare allows you to sort a collection of Stuff instances alphabetically.E.ValueCompare allows you to sort a collection of Stuff instances in ascending numeric order.F.If you changed both occurrences of “compare()“ to “compareTo()“, the code would compile.23.Given: 3.
46、 public class Chopper 4. String a = “12b“; 5. public static void main(String args) 6. System.out.println (new Chopper().chop(args0); 7. 8. int chop(String a) 9. if(a = null) throw new IllegalArgumentException(); 10. return Integer.parseInt(a); 11. And, if the code compiles, the invocation: java Chop
47、per What is the result?（分数：2.50）A.12B.12bC.Compilation fails.D.A NullPointerException is thrown.E.A NumberFormatException is thrown.F.An IllegalArgumentException is thrown.G.An ArrayIndexOutOfBoundsException is thrown.24.Which, concerning command-line options, are true? (Choose all that apply.)（分数：2
48、.50）A.The -D flag is used in conjunction with a name-value pair.B.The -D flag can be used with javac to set a system property.C.The -d flag can be used with java to disable assertions.D.The -d flag can be used with javac to specify where to place .class files.E.The -d flag can be used with javac to document the locations of deprecated APIs in source files.25.Given that “it, IT“ is the locale code for Italy and that “pt, BR“ is the
