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. double Answer F注釋:short類型的x，除以double類型的y，再乘int的2，所以結果是double類型的。注意第三行的強制轉換，只是轉換了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 d)return 4.0d; Answer :B注意這道題主要考的是方法的overload和override。對于overload，只有參數(shù)列表不同，才做為標準，而返回值和訪問控制關鍵字不能做為標準，所以B錯在方法名相同，但只有返回值不同，這是錯的。C和D是正確的overload。對于override，則訪問控制關鍵字只能更加公有化，異常只能是超類方法拋出的異常的子類，也可以不拋出。返回類型，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) 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.catch.finally的問題。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塊后面的語句將不被執(zhí)行。如果遇到System.exit(1)，則finally塊及其后的語句都不執(zhí)行，整個程序退出，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" 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foo(0)時，執(zhí)行第8條語句，output=1，然后執(zhí)行語句15，output=13，然后是17條，output=134，因為是static類型的變量，所以任何對其值的修改都有效。執(zhí)行第二條foo(1),先執(zhí)行語句5，結果拋出異常，轉到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.out.println("even"); 7） 8）public static int odd(int x)return x%2; 9） what is output? Answer: 編譯錯誤。if中的判斷條件的結果必須是boolean類型的。注意這里說的是結果. 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"); 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，被語句6捕獲，輸出caught IOException，然后呢？然后就結束了唄。71）int i=1,j=10; 2）do 3） if(i+>-j) continue; 4）while(i<5); After 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，執(zhí)行完語句3后，i會+，這時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; 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當執(zhí)行第6行后，仍然有對象指向o，所以o不能滿足條件，當?shù)?條語句被執(zhí)行后，就再也沒有對象指向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. An 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，通過測試的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 main(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" F. the code does not compile G. the program throw an exception Answer: G當執(zhí)行java Test Red Green Blue時，數(shù)組args只有012，運行時ArrayIndexOutOfBoundsException這個異常會被拋出，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 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)都會認為是double類型，所以出錯。說一下A和C的區(qū)別吧，-1系統(tǒng)會認為是一個int類型，把int類型再賦給float類型的foo，當然沒錯了，可C就不同啦，42e1是int類型嗎？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=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只有實例變量系統(tǒng)才給予自動賦默認值的這種待遇 15 1) public class Test 2) public 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. g=g C. d=f D. d.equals(f) E d.equals(g) F. g.equals(4.2); Answer: B=兩邊類型不同不相等。所以A和C不等。equals只能用于引用類型，不能用于基本類型，所以D不對，而且兩邊類型不兼容的話,即使對象的內(nèi)容一樣,也不相等，所以E和F不對。17 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） public static void main(String args) 8） Integer i=new Integer(0); 9） add3(i); 10） System.out.println(i.intValue(); 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） 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.append("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 the output? Answer: javajavactextString是String類型的，具有不變性，語句3其實是創(chuàng)建了一個新的字符串，而不是修改原來的textString，而對于StringBuffer類型的對象，則所有修改都是實在的。所以在語句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.protected 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主要的問題是overload，參數(shù)列表必須不同，方法名相同，訪問控制無限制。也無異常限制。這道題因為是構造器，所以B，D和E不對，因為構造器不能有返回類型。211）public class MethodOver 2） public void setVar(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無訪問控制限制，所以A對，順序也屬于參數(shù)列表，順序不同也一樣是overload，所以C正確，D當然正確了，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=EnclosingOne.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)方法訪問非靜態(tài)內(nèi)類： 方法為： Outer myouter=new Outer();這里的myouter是創(chuàng)建的外部類的對象。 Outer.Inner myinner=myouter.new Inner();myinner是內(nèi)類的對象。 然后再myinner.showName();showName()是外類中的非靜態(tài)方法。（2）非靜態(tài)方法訪問非靜態(tài)內(nèi)類 直接創(chuàng)建該內(nèi)部類的對象：new Inner().showName();（3）靜態(tài)方法訪問靜態(tài)內(nèi)類： 也是直接創(chuàng)建該內(nèi)部類的對象，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 implements Component private Component children; C.public class Species public class Animalprivate Species species; Answer: b"is a "意思為是什么：定義了一個超類和一個子類之間的一種直接關系:子類是超類的一種。也即是繼承的關系24 1)package foo; 2) 3)public class Outer 4)public static class Inner 5) 6) which is true to instantiated(事例) Inner class 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 getVar() D.protected float getVar() E.public float getVar(float f) Answer: a,b,d又是override的問題，參數(shù)列表和返回值以及方法名(好像是費話)必須精確匹配,訪問控制要更公有化,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(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 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=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() 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 synchronized 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 when 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哪一個不加鎖，就從哪一個入手，但這道題全都加鎖了，所以先A。29 1)public class X implements Runnable 2)private 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 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 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”)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=1” followed by “x=2, y=2”) Answer: E這道題有問題，當兩個線程同名時，輸出x=1,y=1，但只一次，而當兩個線程不同名時，輸出就是兩次。理論上加鎖時，線程1會執(zhí)行直到結束，然后線程2才會開始執(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).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 might 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 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 only for once (for example, “x=1, y=1” followed by “x=2, y=2”). Answer D這道題也有問題，當兩個線程同名的情況下，只輸出一次，但當兩個線程不同名的情況下，可以清楚的看到兩個線程是交替執(zhí)行的，x=1,y=1后現(xiàn)可以是任何東西，也可能是另一個線程的x=1,y=1。31class A 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. t.wait(); C. t.join(); D.t.yield(); E.t.notify(); F. a.notify(); G.t.interrupt(); 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 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("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" 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問題的關鍵在于String的不變性，雖然又是substring又是concat的，但都只是創(chuàng)建了一個新的字符串，原本的foo一直都沒有被改變，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.toRadians(42);D. double d = Math.cos(Math.toDegrees(42);E. double d = Math.cosine(Math.toRadians(42); Answer: ctoRadians是把一個角度轉換成一個弧度，cos方法的參數(shù)必須是以弧度表示的。36public class Test public static void main(String args) StringBuffer a=new StringBuffer("A"); StringBuffer b=new StringBuffer("B"); operate(a,b); System.out.println(a+","+b); public static void operate(StringBuffer x, StringBuffer y) x.append(y); y=x; what is the output? Answer: AB,B有些不理解。我只能認為y=x這名語句沒有改變b。37 Given:13. public class Foo 14. public static void main (String args) 15. StringBuffer a = new StringBuffer (“A”);16. StringBuffer b = new StringBuffer (“B”);17. operate (a,b);18. system.out.printIna + “,” +b;19. )20. static void operate (StringBuffer x, StringBuffer y) 21. y.append （x）;22. y = x;23. )24. What is the result?A.The code compiles and prints “A,B”.B.The code compiles and prints “A, BA”. C.The code compiles and prints “AB, B”. D.The code compiles and prints “AB, AB”. E.The code compiles and prints “BA, BA”. F.The code does not compile because “+” cannot be overloaded for stringBuffer. Answer B 38. 1) public class Test 2) public static void main(String args) 3) class Foo 4) public int i=3; 5) 6) Object o=(Object)new Foo(); 7) Foo foo=(Foo)O; 8) System.out.println(foo.i); 9) 10) what is result? A.compile error at line 6 B.compile error at line 7 C.print out 3 Answer: C簡單的說，要訪問變量的時候，看等號左邊，訪問方法的時候看等號右邊，但對于static類型的方法除外。39public class FooBar public static void main(String args) int i=0,j=5; 4) tp: for(;i+) for(;-j)