OCJP(1Z0-851) 類比題分析（四）

Exam : 1Z0-851

Java Standard Edition 6 Programmer Certified Professional Exam

以下分析全都是我自己分析或者參考網上的，定有疏漏，還請大家對我的分析提出質疑。

QUESTION 101

Given:
12. import java.util.*;
13. public class Explorer1 {
14. public static void main(String[] args) {
15. TreeSet<Integer> s = new TreeSet<Integer>();
16. TreeSet<Integer> subs = new TreeSet<Integer>();
17. for(int i = 606; i < 613; i++)
18. if(i%2 == 0) s.add(i);
19. subs = (TreeSet)s.subSet(608, true, 611, true);
20. s.add(609);
21. System.out.println(s + " " + subs);
22. }
23. }
What is the result?
A. Compilation fails.
B. An exception is thrown at runtime.
C. [608, 609, 610, 612] [608, 610]
D. [608, 609, 610, 612] [608, 609, 610]
E. [606, 608, 609, 610, 612] [608, 610]
F. [606, 608, 609, 610, 612] [608, 609, 610]
Answer: F

重複的題目，subset方法返回view，而不是copy

QUESTION 102
Given:
23. Object [] myObjects = {
24. new Integer(12),
25. new String("foo"),
26. new Integer(5),
27. new Boolean(true)
28. };
29. Arrays.sort(myObjects);
30. for(int i=0; i<myObjects.length; i++) {
31. System.out.print(myObjects[i].toString());
32. System.out.print(" ");
33. }
What is the result?
A. Compilation fails due to an error in line 23.
B. Compilation fails due to an error in line 29.
C. A ClassCastException occurs in line 29.
D. A ClassCastException occurs in line 31.
E. The value of all four objects prints in natural order.
Answer: C

sort方法比較的必須是可以轉化成相同的而且實現了Comparable借口的相同對象。

QUESTION 103
Given:
1. public class Donkey {
2. public static void main(String[] args) {
3. boolean assertsOn = false;
4. assert (assertsOn) : assertsOn = true;
5. if(assertsOn) {
6. System.out.println("assert is on");
7. }
8. }
9. }
If class Donkey is invoked twice, the first time without assertions enabled, and the second time with
assertions enabled, what are the results?
A. no output
B. no output
assert is on
C. assert is on
D. no output
An AssertionError is thrown.
E. assert is on
An AssertionError is thrown.
Answer: D

考察assert，如果是斷言有效情況，即assert(false)，就會拋出一個AssertionError 

QUESTION 104
Given:
11. Float pi = new Float(3.14f);
12. if (pi > 3) {
13. System.out.print("pi is bigger than 3. ");
14. }
15. else {
16. System.out.print("pi is not bigger than 3. ");
17. }
18. finally {
19. System.out.println("Have a nice day.");
20. }
What is the result?
A. Compilation fails.
B. pi is bigger than 3.
C. An exception occurs at runtime.
D. pi is bigger than 3. Have a nice day.
E. pi is not bigger than 3. Have a nice day.
Answer: A

finally不是用在這種地方，僅僅在try/catch/finally內使用。

QUESTION 105
Given:
11. public static void main(String[] args) {
12. try {
13. args = null;
14. args[0] = "test";
15. System.out.println(args[0]);
16. } catch (Exception ex) {
17. System.out.println("Exception");
18. } catch (NullPointerException npe) {
19. System.out.println("NullPointerException");
20. }
21. }
What is the result?
A. test
B. Exception
C. Compilation fails.
D. NullPointerException
Answer: C

NullPointerException 是Exception 的子類，在編譯器中會有無法達到（not available）的警告。

QUESTION 106
Given:
22. public void go() {
23. String o = "";
24. z:
25. for(int x = 0; x < 3; x++) {
26. for(int y = 0; y < 2; y++) {
27. if(x==1) break;
28. if(x==2 && y==1) break z;
29. o = o + x + y;
30. }
31. }
32. System.out.println(o);
33. }
What is the result when the go() method is invoked?
A. 00
B. 0001
C. 000120
D. 00012021
E. Compilation fails.
F. An exception is thrown at runtime.
Answer: C

考察break，當x=0,y=0,o=00;

當x=0,y=1,o=0001;

當x=1,y=0,break掉內迴圈，o=0001;

當x=2,y=0,o=000120;

當x=2,y=1,break掉斷點處的外迴圈，o=000120;

QUESTION 107
Given:
12. public class Test {
13. public enum Dogs {collie, harrier};
14. public static void main(String [] args) {
15. Dogs myDog = Dogs.collie;
16. switch (myDog) {
17. case collie:
18. System.out.print("collie ");
19. case harrier:
20. System.out.print("harrier ");
21. }
22. }
23. }
What is the result?
A. collie
B. harrier
C. Compilation fails.
D. collie harrier
E. An exception is thrown at runtime.
Answer: D

switch的參數可以是枚舉常量，沒有break，從17行一直往下執行。

QUESTION 108

Click the Exhibit button. Given:

31. public void method() {
32. A a = new A();
33. a.method1();
34. }
Which statement is true if a TestException is thrown on line 3 of class B?
A. Line 33 must be called within a try block.
B. The exception thrown by method1 in class A is not required to be caught.
C. The method declared on line 31 must be declared to throw a RuntimeException.
D. On line 5 of class A, the call to method2 of class B does not need to be placed in a try/catch block.
Answer: B

由於拋出的是一個RuntimeException，不需要處理，所以不需要try塊，也不需要throws，B對。

而A類中拋出的是一個繼承自Exception的TestException，必須處理。

QUESTION 109
Given:
1. public class Boxer1{
2. Integer i;
3. int x;
4. public Boxer1(int y) {
5. x = i+y;
6. System.out.println(x);
7. }
8. public static void main(String[] args) {
9. new Boxer1(new Integer(4));
10. }
11. }
What is the result?
A. The value "4" is printed at the command line.
B. Compilation fails because of an error in line 5.
C. Compilation fails because of an error in line 9.
D. A NullPointerException occurs at runtime.
E. A NumberFormatException occurs at runtime.
F. An IllegalStateException occurs at runtime.
Answer: D

第五行5. x = i+y;，還沒有為i賦值（此時i為null），無法運算。

QUESTION 110
Given:
11. static class A {
12. void process() throws Exception { throw new Exception(); }
13. }
14. static class B extends A {
15. void process() { System.out.println("B"); }
16. }
17. public static void main(String[] args) {
18. new B().process();
19. }
What is the result?
A. B
B. The code runs with no output.
C. Compilation fails because of an error in line 12.
D. Compilation fails because of an error in line 15.
E. Compilation fails because of an error in line 18.
Answer: A

QUESTION 111
Given:
1. public class Venus {
2. public static void main(String[] args) {
3. int [] x = {1,2,3};
4. int y[] = {4,5,6};
5. new Venus().go(x,y);
6. }
7. void go(int[]... z) {
8. for(int[] a : z)
9. System.out.print(a[0]);
10. }
11. }
What is the result?
A. 1
B. 12
C. 14
D. 123
E. Compilation fails.
F. An exception is thrown at runtime.
Answer: C

int[]... z表示可變參數，而可變的是數組的個數。一共有兩個數組，輸出每個數組的第一個元素。

QUESTION 112
Given:
10. public class Foo {
11. static int[] a;
12. static { a[0]=2; }
13. public static void main( String[] args ) {}
14. }
Which exception or error will be thrown when a programmer attempts to run this code?
A. java.lang.StackOverflowError
B. java.lang.IllegalStateException
C. java.lang.ExceptionInInitializerError
D. java.lang.ArrayIndexOutOfBoundsException
Answer: C

還沒new呢，就賦值。初始化錯誤。

QUESTION 113
Given:
11. class X { public void foo() { System.out.print("X "); } }
12.
13. public class SubB extends X {
14. public void foo() throws RuntimeException {
15. super.foo();
16. if (true) throw new RuntimeException();
17. System.out.print("B ");
18. }
19. public static void main(String[] args) {
20. new SubB().foo();
21. }
22. }
What is the result?
A. X, followed by an Exception.
B. No output, and an Exception is thrown.
C. Compilation fails due to an error on line 14.
D. Compilation fails due to an error on line 16.
E. Compilation fails due to an error on line 17.
F. X, followed by an Exception, followed by B.
Answer: A

多態性，首先是調用的SubB裡面的foo()函數，而執行SubB裡面的foo()函數首先就要super.foo();即調用父類的foo()函數輸出X，後來就會拋出一個異常，回到調用該拋出異常的方法的地方。不會輸出B

QUESTION 121
A company has a business application that provides its users with many different reports:
receivables reports, payables reports, revenue projects, and so on. The company has just purchased
some new, state-of-the-art, wireless printers, and a programmer has been assigned the task of enhancing
all of the reports to use not only the company's old printers, but the new wireless printers as well. When the
programmer starts looking into the application, the programmer discovers that because of the design of the
application, it is necessary to make changes to each report to support the new printers. Which two design
concepts most likely explain this situation? (Choose two.)
A. Inheritance
B. Low cohesion
C. Tight coupling
D. High cohesion
E. Loose coupling
F. Object immutability
Answer: BC

 Low cohesion低內聚 Tight coupling高耦合：以上兩個都是軟體工程該避免的。

QUESTION 122
Given:
2. public class Hi {
3. void m1() { }
4. protected void() m2 { }
5. }
6. class Lois extends Hi {
7. // insert code here
8. }
Which four code fragments, inserted independently at line 7, will compile? (Choose four.)
A. public void m1() { }
B. protected void m1() { }
C. private void m1() { }
D. void m2() { }
E. public void m2() { }
F. protected void m2() { }
G. private void m2() { }
Answer: ABEF

子類重寫，存取修飾詞不能reduce

QUESTION 124
Given:
3. class Employee {
4. String name; double baseSalary;
5. Employee(String name, double baseSalary) {
6. this.name = name;
7. this.baseSalary = baseSalary;
8. }
9. }
10. public class SalesPerson extends Employee {
11. double commission;
12. public SalesPerson(String name, double baseSalary, double commission) {
13. // insert code here
14. }
15. }
Which two code fragments, inserted independently at line 13, will compile? (Choose two.)
A. super(name, baseSalary);
B. this.commission = commission;
C. super();
this.commission = commission;
D. this.commission = commission;
super();
E. super(name, baseSalary);
this.commission = commission;
F. this.commission = commission;
super(name, baseSalary);
G. super(name, baseSalary, commission);
Answer: AE

Employee 類僅有帶參數的構造器，沒有預設構造器，這要注意。所以不能出現super();而且還必須顯式調用父類的帶參數的構造器， super(name, baseSalary);必須出現在構造器的第一句話。

QUESTION 125
A team of programmers is reviewing a proposed API for a new utility class. After some discussion, they
realize that they can reduce the number of methods in the API without losing any functionality. If they
implement the new design, which two OO principles will they be promoting?
A. Looser coupling
B. Tighter coupling
C. Lower cohesion
D. Higher cohesion
E. Weaker encapsulation
F. Stronger encapsulation
Answer: A

內聚：一個模組內各個元素彼此結合的緊密程度
耦合：一個軟體結構內不同模組之間互連程度的度量

這裡減少API數量卻不丟失任何功能，意思是各個模組之間的聯絡很小，互聯程度很低，屬於低耦合。

QUESTION 126
Given:
1. class ClassA {
2. public int numberOfInstances;
3. protected ClassA(int numberOfInstances) {
4. this.numberOfInstances = numberOfInstances;
5. }
6. }
7. public class ExtendedA extends ClassA {
8. private ExtendedA(int numberOfInstances) {
9. super(numberOfInstances);
10. }
11. public static void main(String[] args) {
12. ExtendedA ext = new ExtendedA(420);
13. System.out.print(ext.numberOfInstances);
14. }
15. }
Which statement is true?
A. 420 is the output.
B. An exception is thrown at runtime.
C. All constructors must be declared public.
D. Constructors CANNOT use the private modifier.
E. Constructors CANNOT use the protected modifier.
Answer: A

QUESTION 127
Given:
5. class Building { }
6. public class Barn extends Building {
7. public static void main(String[] args) {
8. Building build1 = new Building();
9. Barn barn1 = new Barn();
10. Barn barn2 = (Barn) build1;
11. Object obj1 = (Object) build1;
12. String str1 = (String) build1;
13. Building build2 = (Building) barn1;
14. }
15. }
Which is true?
A. If line 10 is removed, the compilation succeeds.
B. If line 11 is removed, the compilation succeeds.
C. If line 12 is removed, the compilation succeeds.
D. If line 13 is removed, the compilation succeeds.
E. More than one line must be removed for compilation to succeed.
Answer: C

這個強制類型轉換 (String) build1;不會成功

QUESTION 128
Given:
1. public class TestOne {
2. public static void main (String[] args) throws Exception {
3. Thread.sleep(3000);
4. System.out.println("sleep");
5. }
6. }
What is the result?
A. Compilation fails.
B. An exception is thrown at runtime.
C. The code executes normally and prints "sleep".
D. The code executes normally, but nothing is printed.
Answer: C

QUESTION 129
Given:
1. public class Threads4 {
2. public static void main (String[] args) {
3. new Threads4().go();
4. }
5. public void go() {
6. Runnable r = new Runnable() {
7. public void run() {
8. System.out.print("foo");
9. }
10. };
11. Thread t = new Thread(r);
12. t.start();
13. t.start();
14. }
15. }
What is the result?
A. Compilation fails.
B. An exception is thrown at runtime.
C. The code executes normally and prints "foo".
D. The code executes normally, but nothing is printed.
Answer: B

t.start()是讓線程t開始,已經開始了，不能再次t.start()。會拋出非法狀態異常，IllegalThreadStateException。

QUESTION 130
Which two statements are true? (Choose two.)
A. It is possible for more than two threads to deadlock at once.
B. The JVM implementation guarantees that multiple threads cannot enter into a deadlocked state.
C. Deadlocked threads release once their sleep() method's sleep duration has expired.
D. Deadlocking can occur only when the wait(), notify(), and notifyAll() methods are used incorrectly.
E. It is possible for a single-threaded application to deadlock if synchronized blocks are used incorrectly.
F. If a piece of code is capable of deadlocking, you cannot eliminate the possibility of deadlocking by
inserting invocations of Thread.yield().
Answer: AF

A:超過兩個線程死結是可能發生的。

B:JVM並沒有保證多個線程不進入死結狀態。

C:死結的線程就會釋放僅僅和資源有關，資源少了就會死結，和sleep無關，sleep僅僅是讓線程睡眠。

D:不對，除了這些方法，還有別的，如await,signal,signalAll。

E:單線程的應用怎麼會死結，有沒有別的線程來搶資源。

F:如果一段代碼可以死結，你不能通過插入Thread.yield()消除死結的可能性。

QUESTION 132
Given classes defined in two different files:
1. package util;
2. public class BitUtils {
3. public static void process(byte[] b) { /* more code here */ }
4. }
1. package app;
2. public class SomeApp {
3. public static void main(String[] args) {
4. byte[] bytes = new byte[256];
5. // insert code here
6. }
7. }
What is required at line 5 in class SomeApp to use the process method of BitUtils?
A. process(bytes);
B. BitUtils.process(bytes);
C. util.BitUtils.process(bytes);
D. SomeApp cannot use methods in BitUtils.
E. import util.BitUtils.*; process(bytes);
Answer: C

QUESTION 133
A developer is creating a class Book, that needs to access class Paper. The Paper class is deployed in a
JAR named myLib.jar. Which three, taken independently, will allow the developer to use the Paper class
while compiling the Book class? (Choose three.)
A. The JAR file is located at $JAVA_HOME/jre/classes/myLib.jar.
B. The JAR file is located at $JAVA_HOME/jre/lib/ext/myLib.jar..
C. The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes /foo/
myLib.jar/Paper.class.
D. The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes /foo/
myLib.jar.
E. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -cp /foo/myLib.jar/
Paper Book.java.
F. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -d /foo/myLib.jar
Book.java
G. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -classpath /foo/
myLib.jar Book.java
Answer: BDG