1. Suppose that s1 and s2 are two strings. Which of the statements or expressions are valid? (A) String s3 = s1 + s2; (B) String s3 = s1 - s2; (C) s1 <= s2 (D) s1.compareTo(s2); (E) int m = s1.length();   (A), (C) & (E)   (C), (D) & (E)   (A), (D) & (E)   (D) & (E)   (A), (B) & (C)   Hint Half-n-half Clue   2. Given the class definitions class Base { void display () { System.out.println("Base"); } } class Derived extends Base { void display () { System.out.println("Derived"); } } and objects Base b = new Base(); Derived d = new Derived(); Base bd = new Derived; then the print statements System.out.print(b.display() + " "); System.out.print(d.display() + " "); System.out.print(bd.display() + " "); System.out.println(); will display:   Base Base Derived   Derived Derived Derived   Base Derived Base   Base Derived Derived   Half-n-half Clue   3. When we implement the Runnable interface, we must define the method   init()   resume()   start()   run()   main()   Half-n-half Clue   4. Which of the following statements are true? (A) A Java monitor must either extend Thread or implement Runnable. (B) The sleep() method should be enclosed in try ... catch block. (C) The yield() method should be enclosed in try ... catch block. (D) A thread can be temporarily suspended from running by using the wait() method. (E) A suspended thread using suspend() method can be revived using the resume() method.   (B), (D) & (E)   (A), (B) & (D)   (A), (B), (D) & (E)   (C), (D) & (E)   (D) & (E)   Half-n-half Clue   5. Which of the following statements are valid array declaration? (A) int number(); (B) float average[]; (C) double[] marks; (D) counter int[];   (B) & (C)   (A)   (D)   (A) & (C)   Half-n-half Clue   6. Given the following code: class Base { int x = 10; } class Derived extends Base { int x = 20; } Base b = new Base(); Derived d = new Derived ( ); Base bd = new Derived(); The statement System.out.println(b.x + " " + d.x + " " + bd.x); will produce the output   10 20 10   20 10 20   10 20 20   20 20 10   Half-n-half Clue   7. Consider the following code int number[] = new int[5]; After execution of this statement, which of the following are true? (A) number[0] is undefined (B) number[5] is undefined (C) number[4] is null (D) number[2] is 0 (E) number.length() is 5   (E)   (B), (D) & (E)   (C) & (E)   (A) & (E)   Half-n-half Clue