1、【精品文檔】如有侵權(quán)，請(qǐng)聯(lián)系網(wǎng)站刪除，僅供學(xué)習(xí)與交流ocjp考試題庫(kù).精品文檔.1. Given:1. public class returnIt 2. returnType methodA(byte x, double y)3. return (short) x/y * 2;4. 5. What is the valid returnType for methodA in line 2?A. intB. byteC. longD. shortE. floatF. doubleAnswer F注釋:short類(lèi)型的x，除以double類(lèi)型的y，再乘int的2，所以結(jié)果是double類(lèi)型的。注意

2、第三行的強(qiáng)制轉(zhuǎn)換，只是轉(zhuǎn)換了x。2. 1) class Super 2) public float getNum()return 3.0f; 3) 4) 5) public class Sub extends Super 6) 7) which method, placed at line 6, will cause a compiler error? A. public float getNum()return 4.0f; B. public void getNum() C. public void getNum(double d) D. public double getNum(float

3、 d)return 4.0d; Answer :B注意這道題主要考的是方法的overload和override。對(duì)于overload，只有參數(shù)列表不同，才做為標(biāo)準(zhǔn)，而返回值和訪問(wèn)控制關(guān)鍵字不能做為標(biāo)準(zhǔn)，所以B錯(cuò)在方法名相同，但只有返回值不同，這是錯(cuò)的。C和D是正確的overload。對(duì)于override，則訪問(wèn)控制關(guān)鍵字只能更加公有化，異常只能是超類(lèi)方法拋出的異常的子類(lèi)，也可以不拋出。返回類(lèi)型，參數(shù)列表必須精確匹配。所以A是正確的override。3. 1)public class Foo 2) public static void main(String args) 3) tryreturn

4、; 4) finally System.out.println("Finally"); 5) 6) what is the result? A. The program runs and prints nothing.B. The program runs and prints “Finally”.C. The code compiles, but an exception is thrown at runtime.D. The code will not compile because the catch block is missing.Answer:btry.catc

5、h.finally的問(wèn)題。程序中如果遇到return，則finally塊先被執(zhí)行，然后再執(zhí)行retrun，而finally塊后面的語(yǔ)句將不被執(zhí)行。如果遇到System.exit(1)，則finally塊及其后的語(yǔ)句都不執(zhí)行，整個(gè)程序退出，還執(zhí)行什么呀。4. 1） public class Test 2） public static String output="" 3） public static void foo(int i) 4） try 5） if(i=1) 6） throw new Exception(); 7） 8） output +="1"

6、9） 10） catch(Exception e) 11） output+="2" 12） return; 13） 14） finally 15） output+="3" 16） 17） output+="4" 18） 19） public static void main(String args) 20） foo(0); 21） foo(1); 22） 23） 24） what is the value of output at line 22? Asnwer:13423執(zhí)行第一個(gè)foo(0)時(shí)，執(zhí)行第8條語(yǔ)句，output=1，然

7、后執(zhí)行語(yǔ)句15，output=13，然后是17條，output=134，因?yàn)槭莝tatic類(lèi)型的變量，所以任何對(duì)其值的修改都有效。執(zhí)行第二條foo(1),先執(zhí)行語(yǔ)句5，結(jié)果拋出異常，轉(zhuǎn)到catch塊，output=1342，finally任何情況下都執(zhí)行，所以output=13423，然后return跳出方法體，所以output=134235 1）public class IfElse 2）public static void main(String args) 3）if(odd(5) 4）System.out.println("odd"); 5）else 6）System

8、.out.println("even"); 7） 8）public static int odd(int x)return x%2; 9） what is output? Answer: 編譯錯(cuò)誤。if中的判斷條件的結(jié)果必須是boolean類(lèi)型的。注意這里說(shuō)的是結(jié)果.6 1）class ExceptionTest 2）public static void main(String args) 3）try 4）methodA(); 5）catch(IOException e) 6）System.out.println("caught IOException"

9、); 7）catch(Exception e) 8）System.out.println("caught Exception"); 9） 10） 11） If methodA() throws a IOException, what is the result? Answer: caught IOException如果methodA()拋出IOExecption，被語(yǔ)句6捕獲，輸出caught IOException，然后呢？然后就結(jié)束了唄。71）int i=1,j=10; 2）do 3） if(i+>-j) continue; 4）while(i<5); Af

10、ter Execution, what are the value for i and j? A. i=6 j=5 B. i=5 j=5 C. i=6 j=4 D. i=5 j=6 E. i=6 j=6 Answer: d程序一直循環(huán)，直到i=4，j=6時(shí)，執(zhí)行完語(yǔ)句3后，i會(huì)+，這時(shí)i就等于了5，continue后就不能再循環(huán)了，所以選D。81)public class X 2) public Object m() 3) Object o=new Float(3.14F); 4) Object oa=new Object1; 5) oa0=o; 6) o=null; 7) oa0=null;

11、 8） System.out.println(oa0); 9) 10) which line is the earliest point the object a refered is definitely elibile to be garbage collectioned? A.After line 4 B. After line 5 C.After line 6 D.After line 7 E.After line 9(that is,as the method returns) Answer: d當(dāng)執(zhí)行第6行后，仍然有對(duì)象指向o，所以o不能滿足條件，當(dāng)?shù)?條語(yǔ)句被執(zhí)行后，就再也沒(méi)有對(duì)

12、象指向o了，所以選D。9 1) interface Foo 2) int k=0; 3) 4) public class Test implements Foo 5) public static void main(String args) 6) int i; 7) Test test =new Test(); 8) i=test.k; 9) i=Test.k; 10) i=Foo.k; 11) 12) What is the result?A. Compilation succeeds.B. An error at line 2 causes compilation to fail.C. A

13、n error at line 9 causes compilation to fail.D. An error at line 10 causes compilation to fail.E. An error at line 11 causes compilation to fail.Answer: A編譯通過(guò)，通過(guò)測(cè)試的10 what is reserved(保留) words in java? A. run B. default C. implement D. import Answer: b，D111）public class Test 2） public static void m

14、ain(String args) 3） String foo=args1; 4） Sring bar=args2; 5） String baz=args3; 6） 7） java Test Red Green Blue what is the value of baz? A. baz has value of "" B. baz has value of null C. baz has value of "Red" D. baz has value of "Blue" E. baz has value of "Green&q

15、uot; F. the code does not compile G. the program throw an exception Answer: G當(dāng)執(zhí)行java Test Red Green Blue時(shí)，數(shù)組args只有012，運(yùn)行時(shí)ArrayIndexOutOfBoundsException這個(gè)異常會(huì)被拋出，數(shù)組越界。12int index=1; int foo=new int3; int bar=fooindex; int baz=bar+index; what is the result? A. baz has a value of 0 B. baz has value of 1

16、 C. baz has value of 2 D. an exception is thrown E. the code will not compile Answer: b數(shù)組初始化后默認(rèn)值是0，所以baz=0+1=113 which three are valid declaraction（行為） of a float? A. float foo= -1; B. float foo=1.0; C. float foo=42e1; D. float foo=2.02f; E. float foo=3.03d; F. float foo=0x0123; Answer: A，D，F(xiàn)其它的系統(tǒng)都會(huì)

17、認(rèn)為是double類(lèi)型，所以出錯(cuò)。說(shuō)一下A和C的區(qū)別吧，-1系統(tǒng)會(huì)認(rèn)為是一個(gè)int類(lèi)型，把int類(lèi)型再賦給float類(lèi)型的foo，當(dāng)然沒(méi)錯(cuò)了，可C就不同啦，42e1是int類(lèi)型嗎？141）public class Foo 2） public static void main(String args) 3） String s; 4） System.out.println("s="+s); 5） 6） what is the result? A. The code compiles and “s=” is printed.B. The code compiles and “s=

18、null” is printed.C. The code does not compile because string s is not initialized（初始化）. D. The code does not compile because string s cannot be referenced（引用）.E. The code compiles, but a NullPointerException is thrown when toString is called.Answer:C只有實(shí)例變量系統(tǒng)才給予自動(dòng)賦默認(rèn)值的這種待遇15 1) public class Test 2) p

19、ublic static void main(String args) 3) int i=oxFFFFFFF1; 4) int j=i; 5) 6) 7) which is decimal value of j at line 5? A. 0 B.1 C.14 D.-15 E. compile error at line 3 F. compile error at line 4 Answer: C算一算就知道了。16 float f=4.2F; Float g=new Float(4.2F); Double d=new Double(4.2); Which are true? A. f=g B

20、. g=g C. d=f D. d.equals(f) E d.equals(g) F. g.equals(4.2); Answer: B=兩邊類(lèi)型不同不相等。所以A和C不等。equals只能用于引用類(lèi)型，不能用于基本類(lèi)型，所以D不對(duì)，而且兩邊類(lèi)型不兼容的話,即使對(duì)象的內(nèi)容一樣,也不相等，所以E和F不對(duì)。17 1）public class Test 2） public static void add3(Integer i) 3） int val=Value(); 4） val+=3; 5） i=new Integer(val); 6） 7） public static void ma

21、in(String args) 8） Integer i=new Integer(0); 9） add3(i); 10） System.out.println(Value(); 11） 12） what is the result? A. compile fail B.print out "0" C.print out "3" D.compile succeded but exception at line 3 Answer: b在第五行里，程序又操作了New，重新分配了內(nèi)存空間。所以此i非彼i啦。181）public class Test 2

22、） public static void main(String args) 3） System.out.println(63); /為XOR4） 5） what is output? Answer: 5算唄。191） public class Test 2） public static void stringReplace(String text) 3） text=text.replace('j','l'); 4） 5） public static void bufferReplace(StringBuffer text) 6） text=text.appen

23、d("c"); 7） 8） public static void main(String args) 9） String textString=new String("java"); 10） StringBuffer textBuffer=new StringBuffer("java"); 11） StringReplace(textString); 12） bufferReplace(textBuffer); 13） System.out.println(textString+textBuffer); 14） 15） what is

24、 the output? Answer: javajavactextString是String類(lèi)型的，具有不變性，語(yǔ)句3其實(shí)是創(chuàng)建了一個(gè)新的字符串，而不是修改原來(lái)的textString，而對(duì)于StringBuffer類(lèi)型的對(duì)象，則所有修改都是實(shí)在的。所以在語(yǔ)句6中textBuffer變成了javac，所以輸出為javajavac。201）public class ConstOver 2） public ConstOver(int x, int y, int z) 3） which two overload the ConstOver constructor? A.ConstOver() B.p

25、rotected int ConstOver() C.private ConstOver(int z, int y, byte x) D.public void ConstOver(byte x, byte y, byte z) E.public Object ConstOver(int x, int y, int z) Answer: a,c主要的問(wèn)題是overload，參數(shù)列表必須不同，方法名相同，訪問(wèn)控制無(wú)限制。也無(wú)異常限制。這道題因?yàn)槭菢?gòu)造器，所以B，D和E不對(duì)，因?yàn)闃?gòu)造器不能有返回類(lèi)型。211）public class MethodOver 2） public void setVar

26、(int a, int b, float c) 3） which overload the setVar? A.private void setVar(int a, float c, int b) B.protected void setVar(int a, int b, float c) C.public int setVar(int a, float c, int b)return a; D.public int setVar(int a, float c)return a; Answer: a,c,doverload無(wú)訪問(wèn)控制限制，所以A對(duì)，順序也屬于參數(shù)列表，順序不同也一樣是overl

27、oad，所以C正確，D當(dāng)然正確了，參數(shù)列表明顯不同。22 1）class EnclosingOne 2）public class InsideOne 3） 4）public class InnerTest 5） public static void main(String args) 6） EnclosingOne eo=new EnclosingOne(); 7） /insert code here 8） 9） A.InsideOne ei=eo.new InsideOne(); B.eo.InsideOne ei=eo.new InsideOne(); C.InsideOne ei=Enc

28、losingOne.new InsideOne(); D.InsideOne ei=eo.new InsideOne(); E.EnclosingOne.InsideOne ei=eo.new InsideOne(); Answer: e這里邊的一些形式是固定的。（1）靜態(tài)方法訪問(wèn)非靜態(tài)內(nèi)類(lèi)： 方法為： Outer myouter=new Outer();這里的myouter是創(chuàng)建的外部類(lèi)的對(duì)象。 Outer.Inner myinner=myouter.new Inner();myinner是內(nèi)類(lèi)的對(duì)象。 然后再myinner.showName();showName()是外類(lèi)中的非靜態(tài)方法。（

29、2）非靜態(tài)方法訪問(wèn)非靜態(tài)內(nèi)類(lèi) 直接創(chuàng)建該內(nèi)部類(lèi)的對(duì)象：new Inner().showName();（3）靜態(tài)方法訪問(wèn)靜態(tài)內(nèi)類(lèi)： 也是直接創(chuàng)建該內(nèi)部類(lèi)的對(duì)象，即Inner myinner = new Inner()，或者Outer.Inner myinner = new Outer.Inner()也行得通哦。23 What is "is a" relation? A.public interface Color public class Shapeprivate Color color; B.interface Component class Container imple

30、ments Component private Component children; C.public class Species public class Animalprivate Species species; Answer: b"is a "意思為是什么：定義了一個(gè)超類(lèi)和一個(gè)子類(lèi)之間的一種直接關(guān)系:子類(lèi)是超類(lèi)的一種。也即是繼承的關(guān)系24 1)package foo; 2) 3)public class Outer 4)public static class Inner 5) 6) which is true to instantiated(事例) Inner c

31、lass inside Outer? A. new Outer.Inner() B. new Inner() Answer: a,b25class BaseClass private float x=1.0f; private float getVar()return x; class SubClass extends BaseClass private float x=2.0f; /insert code what are true to override getVar()? A.float getVar() B.public float getVar() C.public double g

32、etVar() D.protected float getVar() E.public float getVar(float f) Answer: a,b,d又是override的問(wèn)題，參數(shù)列表和返回值以及方法名(好像是費(fèi)話)必須精確匹配,訪問(wèn)控制要更公有化,如果拋出異常,那么必須異常本身或其子集或什么都不拋. 26 public class SychTest private int x; private int y; public void setX(int i) x=i; public void setY(int i)y=i; public Synchronized void setXY(

33、int i) setX(i); setY(i); public Synchronized boolean check() return x!=y; Under which conditions will check() return true when called from a different class? A.check() can never return true. B.check() can return true when setXY is callled by multiple threads. C.check() can return true when multiple

34、threads call setX and setY separately. D.check() can only return true if SychTest is changed allow x and y to be set separately. Answer: c 27Given:1. public class SyncTest (2. private int x;3. private int y;4. private synchronized void setX (int i) (x=1;)5. private synchronized void setY (int i) (y=

35、1;)6. public void setXY(int 1)(set X(i); setY(i);)7. public synchronized Boolean check() (return x !=y;)8. )Under which conditions will check () return true when called from a different class? A. Check() can never return trueB. Check() can return true when setXY is called by multiple threadsC. Check

36、() can return true when multiple threads call setX and setY separately. D. Check() can only return true if SyncTest is changed to allow x and y to be set separately. Answer:B 28Given:1. public class SyncTest 2. private int x;3. private int y;4. public synchronized void setX (int i) (x=1;)5. public s

37、ynchronized void setY (int i) (y=1;)6. public synchronized void setXY(int 1)(set X(i); setY(i);)7. public synchronized Boolean check() (return x !=y;)8. )Under which conditions will check () return true when called from a different class?A. Check() can never return true.B. Check() can return true wh

38、en setXY is called by multiple threads.C. Check() can return true when multiple threads call setX and setY separately.D. Check() can only return true if SyncTest is changed to allow x and y to be set separately.Answer: A哪一個(gè)不加鎖，就從哪一個(gè)入手，但這道題全都加鎖了，所以先A。29 1)public class X implements Runnable 2)private

39、int x; 3)private int y; 4)public static void main(String args) 5) X that =new X(); 6) (new Thread(that).start(); 7) (new Thread(that).start(); 9) public synchronized void run() 10) for(;) 11) x+; 12) y+; 13) System.out.println("x="+x+",y="+y); 14) 15) 16) what is the result? A.An

40、 error at line 11 causes compilation to fail.B.Errors at lines 6 and 7cause compilation to fail.C.The program prints pairs of values for x and y that might not always be the same on the same line (for example, “x=2, y=1”)D.The program prints pairs of values for x and y that are always the same on th

41、e same line (for example, “x=1, y=1”. In addition, each value appears twice (for example, “x=1, y=1” followed by “x=1, y=1”)E.The program prints pairs of values for x and y that are always the same on the same line (for example, “x=1, y=1”. In addition, each value appears twice (for example, “x=1, y

42、=1” followed by “x=2, y=2”)Answer: E這道題有問(wèn)題，當(dāng)兩個(gè)線程同名時(shí)，輸出x=1,y=1，但只一次，而當(dāng)兩個(gè)線程不同名時(shí)，輸出就是兩次。理論上加鎖時(shí)，線程1會(huì)執(zhí)行直到結(jié)束，然后線程2才會(huì)開(kāi)始執(zhí)行。30 Click the exhibit button:1. public class X implements Runnable( 2. private int x; 3. private int y; 4. 5. public static void main(Stringargs) 6. X that = new X(); 7. (new Thread(that

43、).start(); 8. (new Thread(that).start(); 9. ) 10. 11. public void run() ( 12. for (;) ( 13. x+; 14. y+; 15. System.out.printIn(“x=” + x + “, y = ” + y); 16. ) 17. ) 18. ) What is the result?A. Errors at lines 7 and 8 cause compilation to fail.B. The program prints pairs of values for x and y that mi

44、ght not always be the same on the same line (for example, “x=2, y=1”).C. The program prints pairs of values for x and y that are always the same on the same line (for example, “x=1, y=1”. In addition, each value appears twice (for example, “x=1, y=1” followed by “x=1, y=1”).D. The program prints pai

45、rs of values for x and y that are always the same on the same line (for example, “x=1, y=1”.) In addition, each value appears only for once (for example, “x=1, y=1” followed by “x=2, y=2”).Answer D這道題也有問(wèn)題，當(dāng)兩個(gè)線程同名的情況下，只輸出一次，但當(dāng)兩個(gè)線程不同名的情況下，可以清楚的看到兩個(gè)線程是交替執(zhí)行的，x=1,y=1后現(xiàn)可以是任何東西，也可能是另一個(gè)線程的x=1,y=1。31class A

46、implements Runnable int i; public void run() try Thread.sleep(5000); i=10; catch(InterruptException e) public static void main(String args) try A a=new A(); Thread t=new Thread(a); t.start(); 17) int j=a.i; 19) catch(Exception e) what be added at line line 17,ensure j=10 at line 19? A. a.wait(); B.

47、t.wait(); C. t.join(); D.t.yield(); E.t.notify(); F. a.notify(); G.errupt(); Answer: c32 Given an ActionEvent, which method allows you to identify the affected component?A. public class getClass()B. public Object getSource()C. public Component getSource()D. public Component getTarget()E. public

48、 Component getComponent()F. public Component getTargetComponent()Answer: c33import java.awt.*; public class X extends Frame public static void main(String args) X x=new X(); x.pack(); x.setVisible(true); public X() setLayout(new GridLayout(2,2); Panel p1=new Panel(); add(p1); Button b1=new Button(&q

49、uot;One"); p1.add(b1); Panel p2=new Panel(); add(p2); Button b2=new Button("Two"); p2.add(b2); Button b3=new Button("Three"); p2.add(b3); Button b4=new Button("Four"); add(b4); when the frame is resized, A.all change height B.all change width C.Button "One&quo

50、t; change height D.Button "Two" change height E.Button "Three" change width F.Button "Four" change height and width Answer: f341)public class X 2) public static void main(String args) 3) String foo="ABCDE" 4) foo.substring(3); 5) foo.concat("XYZ"); 6) 7) what is the value of foo at line 6? Answer: ABCDE問(wèn)題的關(guān)鍵在于String的不變性，雖然又是substring又是concat的，但都只是創(chuàng)建了一個(gè)新的字符串，原本的foo一直都沒(méi)有被改變，也不可能被改變。35Which method is an appropriate way to determine the cosine of 42 degrees?A. double d = Math.cos(42);B. double d = Math.cosine(42);C. double d = Math.cos(Math.t