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单选题 下面程序运行结果( ) public class Alpha{ public void foo(){ System.out.print("A"); } } public class Beta extends Alpha{ public void foo(){ System.out.print("B"); } } public class test{ public static void main(String[] args){ Alpha a = new Beta(); Beta b = (Beta)a; a.foo(); b.foo(); }}
学科：JAVA编程技术
时间：2024-12-17 15:56:19
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题目1单选题
1. public class SimpleCalc{ 2. public int value; 3. public void calculate(){value += 7;} 4. } And: 1. public class MultiCalc extends SimpleCalc{ 2. public void calculate(){value -= 3;} 3. public void calculate(int multiplier){ 4. calculate(); 5. super.calculate(); 6. value *= multiplier; 7. } 8. public static void main(String[] args){ 9. MultiCalc calculator = new MultiCalc(); 10. calculator.calculate(2); 11. System.out.println("Value is: " + calculator.value); 12. } 13. } What is the resultA. 12B. 8C. -12D. Compilation fails
题目2单选题
下面接口声明1-7中,用法错误有几个( ) public interface A { 1. int var=1; 2. public A() { } 3. void method1() { } 4. protected void method2(); 5. static void method3(); 6. static void method4() { } 7. default void method5() { } }A. 3B. 5C. 4D. 6
题目3单选题
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 here 17. } 18. } Which code, inserted at line 16, will cause a java.lang.ClassCastExceptionA. Foo f = (Delta)xB. Foo f = (Alpha)xC. Beta b = (Beta)(Alpha)xD. Alpha a = x
题目4单选题
B是一个抽象类,C是B的非抽象子类,下列创建对象x的语句中正确的是( )A. B b= new C( )B. C x= new B( )C. B b= new B( )D. C x= C( )
题目5单选题
11.public interface A {12. public static final int EASY = 3;13. void doStuff(int t);14.}15.16.public class Test implements A {17. void doStuff(int s) {18. s += A.EASY + ++s;19. System.out.println("s " + s);20. }21. public static void main(String[] args) {22. int x = 5;23. new Test2().doStuff(++x);24. }35.}What is the resultA. Compilation failsB. s 16C. s 10D. s 14
题目6单选题
下面程序运行结果( ) public class Alpha{ public void foo(){ System.out.print("A"); } } public class Beta extends Alpha{ public void foo(){ System.out.print("B"); } } public class test{ public static void main(String[] args){ Alpha a = new Beta(); Beta b = (Beta)a; a.foo(); b.foo(); }}A. BAB. BBC. ABD. AA
题目7单选题
11. class Alpha{ 12. public void foo(){System.out.print("A");} 13. } 14. public class Beta extends Alpha{ 15. public void foo(){System.out.print("B");} 16. public static void main(String[ ] args){ 17. Alpha a = new Beta(); 18. Beta b = (Beta)a; 19. a.foo(); 20. b.foo(); 21. } 22. } What is the resultA. BAB. BBC. AAD. AB
题目8单选题
设B是类,C和D是接口,以下声明正确的是( )A. public interface A implements C extends B { }B. public interface A extends B { }C. public class A implements C extends B { }D. public class A extends B implements C, D { }
题目9单选题
1. interface TestA{ String toString(); } 2. public class Test{ 3. public static void main(String[ ] args){ 4. System.out.println(new TestA(){ 5. public String toString(){return "test";} 6. }); 7. } 8. } What is the resultA. Compilation fails because of an error in line 5B. Compilation fails because of an error in line 4C. testD. null
题目10单选题
11. public interface A{ public void m1(); } 13. class B implements A{ } 14. class C implements A{ public void m1(){ }} 15. class D implements A{ public void m1(int x){ }} 16. abstract class E implements A { } 17. abstract class F implements A { public void m1(){ } } 18. abstract class G implements A { public void m1(int x){ } } What is the resultA. Exactly one class does NOT compileB. Exactly four class does NOT compileC. Exactly three class does NOT compileD. Exactly two class does NOT compile
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