J2SE 知识点巩固提高题.doc

J2SE 知识点巩固提高题选择题解答方式： 1. 写出答案 2. 写出做出选择的理由 3. 简略书写相关知识点要点Question 1Click the Exhibit button.1. public class A 2.3. static int counter = 0;4.5. public static int getInstanceCount() 6. return counter;7. 8.9. public A() 10. +counter;11. 12.13. Given this code from Class B:25.A a1 =new A();26. A a2 =new A();27. A a3 =new A();28. System.out.printIn(A.getInstanceCount() );What is the result?A. Compilation of class A fails.B. Line 28 prints the value 3 to System.out.C. Line 28 prints the value 1 to System.out.D. A runtime error occurs when line 25 executes.E. Compilation fails because of an error on line 28.Question 241. Given:10. class One 11. public One foo() return this; 12. 13. class Two extends One 14. public One foo() return this; 15. 16. class Three extends Two 17. / insert method here18. Which two methods, inserted individually, correctly complete theThree class? (Choose two.)A. public void foo() B. public int foo() return 3; C. public Two foo() return this; D. public Three foo() return this; E. public Object foo() return this; 重写方法返回值不能比父类广。Question 3What will happen when you try compiling and running this code?public class Teststatic int i=10;public static void main(String argv)Test t = new Test();t.myMethod(t);public void myMethod(Test t)int i = 99;function(t);System.out.println(t.i);public void function(Test t)t.i = t.i * 2;static i+;A. 编译错误, 静态方法不能调用实例方法.B. An output of 99C. An output of 198D. An output of 22E. An error at runtimeQuestion 4Given:1. public class Plant 2. private String name;3. public Plant(String name) = name; 4. public String getName() return name; 5. 1. public class Tree extends Plant 2. public void growFruit() 3. public void dropLeaves() 4. Which is true? (choose two)A. The code will compile without changes.B. The code will compile if public Tree() super(“fern”); is added to theTree class.C. The code will compile if public Plant() Tree(); is added to thePlant class.D. The code will compile if public Plant() this(”fern”); is added tothe Plant class.E. The code will compile if public Plant() super(”fern”); is added tothe Plant class.Question 5Given:11. public class Test 12. public static void main(String args) 13. int x =5;14. boolean b1 = true;15. boolean b2 = false;16.17.if(x=4) & !b2)18. System.out.print(”l “);19. System.out.print(”2 “);20. if (b2 = true) & b1)21. System.out.print(”3 “);22. 23. What is the result?A. 2B. 3C. 1 2D. 2 3E. 1 2 3F. Compilation fails.G. Au exceptional is thrown at runtime.Question 6Given:10. interface Foo 11. class Alpha implements Foo 12. class Beta extends Alpha 13. class Delta extends Beta 14. public static void main( String args) 15. Beta x = new Beta();16. / insert code here17. 18. Which code, inserted at line 16, will cause ajava.lang.ClassCastException?A. Alpha a = x;B. Foo f= (Delta)x;C. Foo f= (Alpha)x;D. Beta b = (Beta)(Alpha)x;Question 7Assume that country is set for each class.Given:10. public class Money 11. private String country, name;12. public String getCountry() return country; 13.and:24. class Yen extends Money 25. public String getCountry() return super.country; 26. 27.28. class Euro extends Money 29. public String getCountry(String timeZone) 30. return super.getCountry();31. 32. Which two are correct? (Choose two.)A. Yen returns correct values.B. Euro returns correct values.C. An exception is thrown at runtime.D. Yen and Euro both return correct values.E. Compilation fails because of an error at line 25.F. Compilation fails because of an error at line 30.Question 812. Given:13. public class Pass 14. public static void main(String args) 15. int x=5;16. Pass p = new Pass();17. p.doStuff(x);18. System.out.print(” main x = “+ x);19. 20.21. void doStuff(int x) 22. System.out.print(” doStuff x = “+ x+);23. 24. What is the result?A. Compilation fails.B. An exception is thrown at runtime.C. doStuffx = 6 main x = 6D. doStuffx = 5 main x = 5E. doStuffx = 5 main x = 6F. doStuffx = 6 main x = 5 Question 9Given:1. class TestA 2. public void start() System.out.println(”TestA”); 3. 4. public class TestB extends TestA 5. public void start() System.out.println(”TestB”); 6. public static void main(String args) 7. (TestA)new TestB().start();8. 9. What is the result?A. TestAB. TestBC. Compilation fails.D. An exception is thrown at runtime.Question 10What will happen when you attempt to compile and run this code?abstract class Baseabstract public void myfunc() ;public void another()System.out.println(Another method);public class Abs extends Basepublic static void main(String argv)Base b= new Abs(); /Ab. myfunc(); /Bpublic void myfunc()System.out.println(My Func);public void amethod()myfunc();1 choice1) The code will compile and run, printing out the words My Func2) The compiler will complain error at /A.3) The compiler will complain error at /B.4) The compiler will complain error at other position.Question 11What will be the output when the following code is compiled and run (Assuming written inside main)?String s1 = new String(amit);System.out.println(s1.replace(m,r);System.out.println(s1);String s3 = arit;String s4 = arit;String s2 = s1.replace(m,r);System.out.println(s2 = s3);System.out.println(s3 = s4);1 choiceA. aritamitfalsetrueB. aritarittruetrueC. amitamitfalsefalseD. aritarittruefalseQuestion 12Given:What will happen if you compile/run the following code?class MyClassint x;MyClass(int i)x = i;public static void main(String args)MyClass m1 = new MyClass(100);MyClass m2 = new MyClass(100);System.out.println(m1=m2);if(m1.equals(m2)System.out.println(Both are equal);elseSystem.out.println(Both are not equal);1 choiceA. Compilation error: equals() method was not defined.B. true Both are equalC. false Both are equal.D. true Both are not equal.E. false Both are not equalQuestion 131. public class test 2. public static void add3 (Integer i) 3. int val = Value ( );4. val += 3;5. i = new Integer (val);6. 7.8. public static void main (String args ) 9. Integer i = new Integer (0);10. add3 (i);11. system.out.printIn (Value ( );12. 13. )What is the result?A. Compilation will fail.B. The program prints “0”.C. The program prints “3”.D. Compilation will succeed but an exception will be thrown at line 3.Question 14Given:1. public class ConstOver 2. public ConstOver