Trắc nghiệm Core Java 1. Which of the following statements are valid, given the following variable declarations: boolean a; boolean b; int c; (Select a valid answer) A (a && c) C (a ^ b) | c B (a || a) D (a & c) Answer: B Mark: 1.0 2. Which of the following can be applied to constructors: (Select a valid answer) A final B static C synchronized D None of these. Answer: D Mark: 1.0 3. Which of the following retain their preferred size (width and height) when added (individually) to the North section of a container with a BorderLayout (assume that no other components or containers are present in the North section). (Select a valid answer) A TextArea B Button C TextField D Checkbox Answer: D Mark: 1.0 4. Which of the following are legal names for variables. (Select a valid answer) A int B %large C Integer D 2much Answer: C Mark: 1.0 5. Consider the following piece of code and select the correct statement from the following. String s = new String("abcdefgh"); // (1) s.replace('d', 'q'); // (2) System.out.println(s); // (3) (Select the one right answer) A The code fails to compile, reporting an error at line 2. Strings are immutable, and therefore a replace() method is meaningless. B The code compiles correctly, and displays the text "abcqefgh". C The code compiles correctly, and displays the text "abcdefgh". D The code compiles, but an exception is thrown when line 2 is executed. Answer: C Mark: 1.0 6. Which of the following keywords can be applied to the variables or methods of an interface. (Select all valid answers) A static B private C public D protected Answer: A, C Mark: 0.5 7. Consider the following piece of code and select the correct statement(s): 1. class A{ 2. protected int method(){ 3. } 4. } 5. 6. class B extends A{ 7. int method(){ 8. } 9. } (Select all valid answers) A The code fails to compile, because you can't override a method to be more private than its parent. B The code fails to compile, because method() is declared as protected, and is therefore not available to any subclass. C The code fails to compile. However, it can be made to compile correctly by prefixing line 7 with the access qualifier "protected". D The code fails to compile. However, it can be made to compile correctly by prefixing line 7 with the access qualifier "public". Answer: A, C , D Mark: 1.0 8. Consider the following piece of code (assume the Graphics context g is defined correctly): g.setBackground(Color.red); g.setForeground(Color.white); g.drawLine(10, 10, 50, 10); g.setForeground(Color.blue); g.drawRect(100, 100, 50, 50); What is displayed when this code is executed. (Select a valid answer) A A blue line from (10,10) to (50,10) and a blue rectangle with upper left corner at (100,100). B A white line from (10,10) to (50,10) and a blue square with top left corner at (100,100). C A white line from (10,10) to (10,50) and a blue square with lower left corner at (100,100). D A red line from (10, 10) to (50,10) and a red square with upper left corner at (100,100). Answer: B Mark: 1.0 9. Consider the following piece of code. class Test{ public static void main(String [] args){ System.out.println(args[3]); } } When the following is typed at the command line, what is displayed: (Select a valid answer) java Test Metallica Justice For All A All B For C Justice D Nothing Answer: A Mark: 1.0 10. Consider the following piece of code. 1. String s = "abcd"; 2. Integer x = new Integer(3); 3. String s2 = s + 4; 4. s2 = null; 5. s = null; Following the execution of which line above, is the object referenced by s2 available for garbage collection. (Select the one right answer) A Line 5 B It is not possible to say when an object is available for garbage collection. C Line 4 D The objects are not available until the executing thread is ended. Answer: C Mark: 1.0 11. What is displayed when the following piece of code is compiled and executed: class Test{ public static void main(String [] args){ Base b = new Subclass(); System.out.println(b.x); System.out.println(b.method()); } } class Base{ int x = 2; int method(){ return x; } } class Subclass extends Base{ int x = 3; int method(){ return x; } } (Select the one right answer) A Nothing. The code fails to compile because the object b is not created in a valid way. B 2 3 C 2 D 3 2 3 Answer: B Mark: 1.0 12. What is displayed when the following is executed: String s1 = "aaa"; s1.concat("bbb"); System.out.println(s1); (Select the one right answer) A The string "aaa". B The string "aaabbb". E The string "bbb". D The string "bbbaaa". Answer: A Mark: 0.5 13. What is the output of the following piece of code: 1. int x = 6; 2. double d = 7.7; 3. 4. System.out.println((x > d) ? 99.9 : 9); (Select the one right answer) A 9 B 9.0 C 99.9 D Nothing. An ArithmeticException is thrown at line 4. Answer: B Mark: 1.0 14. Which of the following applet tags are mandatory (select all the correct answers). A CODE B WIDTH C HEIGHT D PARAM Answer: A, B, C Mark: 1.0 15. What is printed out following the execution of the code below: 1. class Test{ 2. static String s; 3. public static void main(String []args){ 4. int x = 4; 5. if (x < 4) 6. System.out.println("Val = " + x); 7. else 8. System.out.println(s); 9. } 10. } (Select the one right answer) A Nothing. The code fails to compile because the String s isn't declared correctly. B The text "Val = null" is displayed. C The string "Val = " is displayed. D The text "null" is displayed Answer: D Mark: 1.0 16. What is displayed when the following piece of code is executed (assume the graphics context, g, is correctly set up): g.drawString("abc", 10, 10); (Select the one right answer) A The text "abc" with the lower left part of "a" located at x = 10, y = 10. B The text "abc" with the upper left part of "a" located at x = 10, y = 10. C Nothing. This is not a valid method. D The text "abc" with the lower right part of "a" located at x = 10, y = 10. Answer: A Mark: 0.5 17. To reference a JAR from a web page, which of the following keywords are used: (Select the one right answer) A jar C zip B class D archive Answer: D Mark: 0.5 18. Analyse the following 2 classes and select the correct statements. class A{ private int x = 0; static int y = 1; protected int q = 2; } class B extends A{ void method(){ System.out.println(x); System.out.println(y); System.out.println(q); } } (Select all valid answers) A The code fails to compile because the variable x is not available to class B. B The code compiles correctly, and the following is displayed: 0 1 2 C The compiler will complain that the variable x in class B is undefined. D Removing the line "System.out.println(x)" will allow the code to compile correctly. Answer: A, C, D Mark: 1.0 19. Which of the following interfaces can be used to manage a collection of elements, with no duplication. (Select the one right answer) A List B Vector C Set D None of them Answer: C Mark: 0.5 20. Which of the following are valid ways to define an abstract method. (Select all valid answers) A abstract void Test(); B abstract void Test() {} C static abstract void Test(); D final abstract void Test(); E Methods cannot be defined as abstract, only variables can be abstract. A abstract void Test(); B Methods cannot be defined as abstract, only variables can be abstract. C abstract static void Test(); D final abstract void Test(); Answer: A Mark: 0.5 . Trắc nghiệm Core Java 1. Which of the following statements are valid, given the following. is typed at the command line, what is displayed: (Select a valid answer) java Test Metallica Justice For All A All B For C Justice D Nothing