J2SE 知识点巩固提高题.docVIP

J2SE 知识点巩固提高题 Question 1 Click 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 2 41. 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 here 18. } Which two methods, inserted individually, correctly complete the Three 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 3 What will happen when you try compiling and running this code? public class Test { static 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 99 C. An output of 198 D. An output of 22 E. An error at runtime Question 4 Given: 1. public class Plant { 2. private String name; 3. public Plant(String name) { this.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 the Tree class. C. The code will compile if pub