Java面试汇总(四)
最全的Java面试题目下载1.Which of the following lines will compile without warning or error.答案（5）1) float f=1.3;2) char c="a";3) byte b=257;4) boolean b=null;5) int i=10;2. What will happen if you try to compile and run the following codepublic class MyClass { public static void main(String arguments[]) { amethod(arguments); } public void amethod(String[] arguments) { System.out.println(arguments); System.out.println(arguments); }}答案（1）1) error Can't make static reference to void amethod.2) error method main not correct3) error array must include parameter4) amethod must be declared with String3. Which of the following will compile without error答案（23）1) import java.awt.*;package Mypackage;class Myclass {}2) package MyPackage;import java.awt.*;class MyClass{}3) /*This is a comment */package MyPackage;import java.awt.*;class MyClass{}4. What will be printed out if this code is run with the following command line?java myprog good morningpublic class myprog{ public static void main(String argv[]) { System.out.println(argv); }}答案（4）1) myprog2) good3) morning4) Exception raised:"java.lang.ArrayIndexOutOfBoundsException: 2" 5. What will happen when you compile and run the following code?public class MyClass{static int i;public static void main(String argv[]){ System.out.println(i);}}答案（4）1) Error Variable i may not have been initialized2) null3) 14) 06. What will happen if you try to compile and run the following code?public class Q {public static void main(String argv[]){ int anar[]=new int[]{1,2,3}; System.out.println(anar);}}答案（3）1) 12) Error anar is referenced before it is initialized3) 24) Error: size of array must be defined7. What will happen if you try to compile and run the following code?public class Q {public static void main(String argv[]){ int anar[]=new int; System.out.println(anar);}}答案（3）1) Error: anar is referenced before it is initialized2) null3) 04) 58. What will be the result of attempting to compile and run the following code?答案（3）abstract class MineBase {abstract void amethod();static int i;}public class Mine extends MineBase {public static void main(String argv[]){int[] ar=new int;for(i=0;i < ar.length;i++) System.out.println(ar);}}1) a sequence of 5 0's will be printed2) Error: ar is used before it is initialized3) Error Mine must be declared abstract4) IndexOutOfBoundes Error9. What will be printed out if you attempt to compile and run the following code ?int i=1;switch (i) {case 0: System.out.println("zero"); break;case 1: System.out.println("one");case 2: System.out.println("two");default: System.out.println("default");}答案（3）1) one2) one, default3) one, two, default4) default10. Which of the following lines of code will compile without error答案（23）1) int i=0;if(i) { System.out.println("Hello"); }2) boolean b=true;boolean b2=true;if(b==b2) { System.out.println("So true"); }3) int i=1;int j=2;if(i==1|| j==2) System.out.println("OK");4) int i=1;int j=2;if(i==1 &| j==2) System.out.println("OK");11. What will be output if you try to compile and run the following code, but there is no file called Hello.txt in the current directory?.import java.io.*;public class Mine{public static void main(String argv[]){ Mine m=new Mine(); System.out.println(m.amethod()); }public int amethod(){ try{ FileInputStream dis=new FileInputStream("Hello.txt"); }catch (FileNotFoundException fne){ System.out.println("No such file found"); return -1; }catch(IOException ioe){}finally{ System.out.println("Doing finally"); } return 0; }}答案（3）1) No such file found2 No such file found ,-13) No such file found, Doing finally, -14) 012.Which of the following statements are true?答案（1）1) Methods cannot be overriden to be more private2) static methods cannot be overloaded3) private methods cannot be overloaded4) An overloaded method cannot throw exceptions not checked in the base class13.What will happen if you attempt to compile and run the following code?答案（3）class Base {}class Sub extends Base {}class Sub2 extends Base {}public class CEx{ public static void main(String argv[]){Base b=new Base();Sub s=(Sub) b; }}1) Compile and run without error2) Compile time Exception3) Runtime Exception14.Which of the following statements are true?答案（123）1) System.out.println( -1 >>> 2);will output a result larger than 102) System.out.println( -1 >>> 2); will output a positive number3) System.out.println( 2 >> 1); will output the number 14) System.out.println( 1 <<< 2); will output the number 415.What will happen when you attempt to compile and run the following code?public class Tux extends Thread{ static String sName = "vandeleur"; public static void main(String argv[]){ Tux t = new Tux(); t.piggy(sName); System.out.println(sName); } public void piggy(String sName){ sName = sName + " wiggy"; start(); } public void run(){ for(int i=0;i < 4; i++){ sName = sName + " " + i; } }}答案（4）1) Compile time error2) Compilation and output of "vandeleur wiggy"3) Compilation and output of "vandeleur wiggy 0 1 2 3"4) Compilation and output of either "vandeleur", "vandeleur 0", "vandeleur 0 1" "vandaleur 0 1 2" or "vandaleur 0 1 2 3"16.What will be displayed when you attempt to compile and run the following code//Code startimport java.awt.*;public class Butt extends Frame{ public static void main(String argv[]){ Butt MyBut=new Butt(); } Butt(){ Button HelloBut=new Button("Hello"); Button ByeBut=new Button("Bye"); add(HelloBut); add(ByeBut); setSize(300,300); setVisible(true); }}//Code end答案（3）1) Two buttons side by side occupying all of the frame, Hello on the left and Bye on the right2) One button occupying the entire frame saying Hello3) One button occupying the entire frame saying Bye4) Two buttons at the top of the frame one saying Hello the other saying Bye17.What will be output by the following code?public class MyFor{ public static void main(String argv[]){ int i; int j; outer: for (i=1;i <3;i++) inner: for(j=1; j<3; j++) { if (j==2) continue outer; System.out.println("Value for i=" + i + " Value for j=" +j); } }}答案（12）1) Value for i=1 Value for j=12) Value for i=2 Value for j=13) Value for i=2 Value for j=24) Value for i=3 Value for j=118.Which statement is true of the following code?public class Agg{public static void main(String argv[]){ Agg a = new Agg(); a.go();}public void go(){ DSRoss ds1 = new DSRoss("one"); ds1.start();}}class DSRoss extends Thread{private String sTname="";DSRoss(String s){sTname = s;}public void run(){notwait();System.out.println("finished");}public void notwait(){while(true){ try{ System.out.println("waiting"); wait(); }catch(InterruptedException ie){} System.out.println(sTname); notifyAll(); }}}答案（4）1) It will cause a compile time error2) Compilation and output of "waiting"3) Compilation and output of "waiting" followed by "finished"4) Runtime error, an exception will be thrown19.Which of the following methods can be legally inserted in place of the comment //Method Here ?class Base{public void amethod(int i) { }}public class Scope extends Base{public static void main(String argv[]){}//Method Here}答案（23）1) void amethod(int i) throws Exception {}2) void amethod(long i)throws Exception {}3) void amethod(long i){}4) public void amethod(int i) throws Exception {}20.You have created a simple Frame and overridden the paint method as followspublic void paint(Graphics g){g.drawString("Dolly",50,10);}What will be the result when you attempt to compile and run the program?答案（3）1) The string "Dolly" will be displayed at the centre of the frame2) An error at compilation complaining at the signature of the paint method3) The lower part of the word Dolly will be seen at the top of the frame, with the top hidden.4) The string "Dolly" will be shown at the bottom of the frame.21.What will be the result when you attempt to compile this program?public class Rand{ public static void main(String argv[]){int iRand;iRand = Math.random();System.out.println(iRand); }}答案（1）1) Compile time error referring to a cast problem2) A random number between 1 and 103) A random number between 0 and 14) A compile time error about random being an unrecognised method22.Given the following codeimport java.io.*;public class Th{ public static void main(String argv[]){Th t = new Th();t.amethod(); } public void amethod(){try{ ioCall();}catch(IOException ioe){} }}What code would be most likely for the body of the ioCall method答案（1）1) public void ioCall ()throws IOException{DataInputStream din = new DataInputStream(System.in);din.readChar();}2) public void ioCall ()throw IOException{DataInputStream din = new DataInputStream(System.in);din.readChar();}3) public void ioCall (){DataInputStream din = new DataInputStream(System.in);din.readChar();}4) public void ioCall throws IOException(){DataInputStream din = new DataInputStream(System.in);din.readChar();}23.What will happen when you compile and run the following code?public class Scope{ private int i; public static void main(String argv[]){Scope s = new Scope();s.amethod(); }//End of main public static void amethod(){System.out.println(i); }//end of amethod}//End of class答案（3）1) A value of 0 will be printed out2) Nothing will be printed out3) A compile time error4) A compile time error complaining of the scope of the variable i24.You want to lay out a set of buttons horizontally but with more space between the first button and the rest. You are going to use the GridBagLayout manager to control the way the buttons are set out. How will you modify the way the GridBagLayout acts in order to change the spacing around the first button?答案（2）1) Create an instance of the GridBagConstraints class, call the weightx() method and then pass the GridBagConstraints instance with the component to the setConstraints method of the GridBagLayout class.2) Create an instance of the GridBagConstraints class, set the weightx field and then pass the GridBagConstraints instance with the component to the setConstraints method of the GridBagLayout class.3) Create an instance of the GridBagLayout class, set the weightx field and then call the setConstraints method of the GridBagLayoutClass with the component as a parameter.4) Create an instance of the GridBagLayout class, call the setWeightx() method and then pass the GridBagConstraints instance with the component to the setConstraints method of the GridBagLayout class.25.Which of the following can you perform using the File class?答案（23）1) Change the current directory2) Return the name of the parent directory3) Delete a file4) Find if a file contains text or binary information26.Which statement is true of the following code?public class Rpcraven{public static void main(String argv[]){Pmcraven pm1 = new Pmcraven("One");pm1.run();Pmcraven pm2 = new Pmcraven("Two");pm2.run();}}class Pmcraven extends Thread{private String sTname="";Pmcraven(String s){sTname = s;}public void run(){for(int i =0; i < 2 ; i++){ try{ sleep(1000); }catch(InterruptedException e){} yield(); System.out.println(sTname); }}}答案（2）1) Compile time error, class Rpcraven does not import java.lang.Thread2) Output of One One Two Two3) Output of One Two One Two4) Compilation but no output at runtime27.You are concerned that your program may attempt to use more memory than is available. To avoid this situation you want to ensure that the Java Virtual Machine will run its garbage collection just before you start a complex routine. What can you do to be certain that garbage collection will run when you want .答案（1）1) You cannot be certain when garbage collection will run2) Use the Runtime.gc() method to force garbage collection3) Ensure that all the variables you require to be garbage collected are set to null4) Use the System.gc() method to force garbage collection28、Which statements about the garbage collection are true?答案（2）1. The program developer must create a thread to be responsible for free the memory.2. The garbage collection will check for and free memory no longer needed.3. The garbage collection allow the program developer to explicity and immediately free the memory.4. The garbage collection can free the memory used java object at expect time.29.You have these files in the same directory. What will happen when you attempt to compile and run Class1.java if you have not already compiled Base.java//Base.javapackage Base;class Base{ protected void amethod(){System.out.println("amethod"); }//End of amethod}//End of class basepackage Class1;//Class1.javapublic class Class1 extends Base{ public static void main(String argv[]){Base b = new Base();b.amethod(); }//End of main}//End of Class1答案（4）1) Compile Error: Methods in Base not found2) Compile Error: Unable to access protected method in base class3) Compilation followed by the output "amethod"4)Compile error: Superclass Class1.Base of class Class1.Class1 not found30.What will happen when you attempt to compile and run the following codeclass Base{ private void amethod(int iBase){System.out.println("Base.amethod"); }}class Over extends Base{ public static void main(String argv[]){Over o = new Over();int iBase=0;o.amethod(iBase);} public void amethod(int iOver){ System.out.println("Over.amethod"); }}答案（4）1) Compile time error complaining that Base.amethod is private2) Runtime error complaining that Base.amethod is private3) Output of "Base.amethod"4) Output of "Over.amethod"一个袋子中有100个黑球，100个白球，每次从中取出两个球，然后放回一个球，如果取出两个球颜色相同，则放入一个黑球，如果取出一百一黑，则放入一个白球，请问到最后袋中剩下的球的颜色：1）黑球 2）白球 3）不一定。 黑球给出证明。建立一个数据库模型，用于管理一个公司部门及其内部雇员，每个部门都有一个负责人。根据你的数据库模型，编写sql语句建立你的数据库表，给出一个雇员的姓名，查询该雇员所属的部门负责人。1. 5）2. 1）3. 2）3）4. 4）5. 4)6. 3)7. 3)8. 3)9. 3)10. 2)3)11. 3)12. 1)13. 3)14. 1)2)3)15. 4)16. 3)17. 1)2)18. 4)19. 2)3)20. 3)21. 1)22. 1)23. 3)24. 2)25. 2,326. 2)27. 1)28. 229. 430. 4黑球。Java试题(二)(时间40分钟)一、 选择：1． 欲构造ArrayList类的一个实例，此类继承了List接口，下列哪个方法是正确的？A.ArrayList myList=new object(); B.List myList=new ArrayList();C.ArrayList myList=new List(); D.List myList=new List();2． 指出正确的表达式。A.byte b=128; B.Boolean b=null;C.long=0xfffL D.double=0.9239d3． 指出下列程序运行的结果。public class Example{ String str=new String (“good”); char[]ch={‘a’,’b’,’c’}; public static void main(String args[]) { Example ex=new example(); ex.change(ex.str,ex.ch); System.out.print(ex.str=” and ”); System.out.print(ex.ch);}public void change(String str,char ch[]) { str=”test ok”; ch=’g’;}}A.good and abc B.good and gbcC.test ok and abc D.test ok ang gbc4． 运行下列程序，会产生什么结果？public class X extends Thread implements Rumble{ public void run() { System.out.println(“this is run()”); } public static void main(String args[]) { Thread t=new Thread (new X()); t.start(); }}A.第一行会产生编译错误 B.第六行会产生编译错误C.第六行会产运行错误 D.程序会运行和启动5． 哪个关键字可以对对象加互斥锁？A.transient B.synchronizedC.serialize D.static6． 下列代码哪一行会出错？1) public void modify() {2) int I,j,k;3) I=100;4) while (I>0) {5) j=I*2;6) System.out.println(“ The value of j is ”+j);7) k=k+1;8) I--;9) }10) }A.line 4 B.line 6C.line 7 D.line 8二、 多面选择1． public class parent { int change() {}}class Child extends Parent{}哪些方法可以加入类Child中？A.public int change() {} B.int chang (int i) {}C.private int change () {} D.abstract int chang () {}2． String s = “hello”;String t = “hello”;char c[] ={‘h’,’e’,’l’,’l’,’o’};下列哪些表达式返回true？A.s.equals(t); B.t.equals(c);C.s==t; D.t.equals(new String (“hello”));3． 给出下面代码段：1． switch(m)2． { case 0: System.out.println(“case 0”);3． case1: System.out.println(“case 1”); break;4． case2:5． default:System.out.println(“default”);6． }下面m的哪些值将引起”default”的输出？A.0 B.1C.2 D.34．对于下列代码：public class Sample { long length; public Sample (long 1) {length = 1;} public static void main(String arg[]) { Sample s1,s2,s3; s1 = new Sample(21L); s2 = new Sample(21L); s3 = s2; long m = 21L; }}下列哪些表达式返回值为‘true’?A.s1==s2; B. s2==s3;C.m==s1; D.s1.equals(m)5．给定下面的代码片段：public void Test() { try { method(); System.out.println(“Hello World”); } catch (ArrayIndexOutOfBoundsException e) { System.out.println(“Exception1”); } finally { System.out.println(“Thank you!”); }}如果函数method正常运行并返回，会显示下面的哪些信息？A. Hello World B.ExceptionC.Exception1 D.Thank you!6．关于session的论述正确的有：A.一个session可以对应数个用户B.一个session只能对应一个用户C.可以手动关闭一个sessionD.session如果不手动关闭，会一直存在Server中三、填空题：1．请描述一下Test.java编译后，在控制台执行命令“java Test”后的输出结果：_________ABA_____________Test.java内容如下：class A{ public A() { System.out.print(“A”);}}class B extends A{ public B() { System.out.print(“B”); A a=new A();}}public class Test{ public Test(){ System.out.print(“Test”);}public static void main(String[] a){ B b=new B();}}2．下列代码不能编译的原因是：______Static Problem_______________Class A { Private int x; Public static void main(String args[]) { new B();}class B{ B() {System.out.println(x);}}}4． 下面程序建立一个服务器通过监听8080端口向客户端输出”Welcome!”字符串，请补充缺少的程序片断：public class WelcomeServer{public static void main(String[] a) throws I0exception{ ____1__ServerSocket so; System.out.println(“WelcomeServer started!”); while(true) { Socket client = ____2____; System.out.println(“A client come!”); try { PrintWriter writer = new PrintWriter( new BufferedWriter(____3____(____4____))); writer.println(“Welcome!”); } catch (I0Exception ioe2) { System.out.println(“Something error!”); } } }}
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