1. Which interface provides the capability to store objects using a key-value pair?
2. Which collection class allows you to associate its elements with key values, and allows you to retrieve objects in FIFO (first-in, first-out) sequence?
3. Which collection class allows you to access its elements by associating a key with an element's value, and provides synchronization?
4. Which is valid declaration of a float?
5. / Missing Statement ? / public class foo { public static void main(String[]args)throws Exception { java.io.PrintWriter out = new java.io.PrintWriter(); new java.io.OutputStreamWriter(System.out,true); out.println("Hello"); } } What line of code should replace the missing statement to make this program compile?
6. What is the numerical range of char?
7. Which of the following are Java reserved words? run import default implement
8. What will be the output of the program? public class Test { public static void main (String[] args) { String foo = args[1]; String bar = args[2]; String baz = args[3]; System.out.println("baz = " + baz); / Line 8 / } } And the command line invocation: > java Test red green blue
9. What will be the output of the program? public class Test { public static void main (String args[]) { String str = NULL; System.out.println(str); } }
10. What will be the output of the program? package foo; import java.util.Vector; / Line 2 / private class MyVector extends Vector { int i = 1; / Line 5 / public MyVector() { i = 2; } } public class MyNewVector extends MyVector { public MyNewVector () { i = 4; / Line 15 / } public static void main (String args []) { MyVector v = new MyNewVector(); / Line 19 / } }
11. What will be the output of the program? public class Test { private static int[] x; public static void main(String[] args) { System.out.println(x[0]); } }
12. What will be the output of the program? import java.util.; class I { public static void main (String[] args) { Object i = new ArrayList().iterator(); System.out.print((i instanceof List)+","); System.out.print((i instanceof Iterator)+","); System.out.print(i instanceof ListIterator); } }
13. What will be the output of the program? public class Test { private static float[] f = new float[2]; public static void main (String[] args) { System.out.println("f[0] = " + f[0]); } }
14. What will be the output of the program? import java.util.; class H { public static void main (String[] args) { Object x = new Vector().elements(); System.out.print((x instanceof Enumeration)+","); System.out.print((x instanceof Iterator)+","); System.out.print(x instanceof ListIterator); } }
15. What will be the output of the program? TreeSet map = new TreeSet(); map.add("one"); map.add("two"); map.add("three"); map.add("four"); map.add("one"); Iterator it = map.iterator(); while (it.hasNext() ) { System.out.print( it.next() + " " ); }
16. What will be the output of the program? public static void main(String[] args) { Object obj = new Object() { public int hashCode() { return 42; } }; System.out.println(obj.hashCode()); }
17. class Test1 { public int value; public int hashCode() { return 42; } } class Test2 { public int value; public int hashcode() { return (int)(value^5); } } which statement is true?
18. Which statement is true for the class java.util.HashSet?
19. Which of the following statements about the hashcode() method are incorrect? The value returned by hashcode() is used in some collection classes to help locate objects. The hashcode() method is required to return a positive int value. The hashcode() method in the String class is the one inherited from Object. Two new empty String objects will produce identical hashcodes.
20. What two statements are true about properly overridden hashCode() and equals() methods? hashCode() doesn't have to be overridden if equals() is. equals() doesn't have to be overridden if hashCode() is. hashCode() can always return the same value, regardless of the object that invoked it. equals() can be true even if it's comparing different objects.
21. Which two statements are true about comparing two instances of the same class, given that the equals() and hashCode() methods have been properly overridden? If the equals() method returns true, the hashCode() comparison == must return true. If the equals() method returns false, the hashCode() comparison != must return true. If the hashCode() comparison == returns true, the equals() method must return true. If the hashCode() comparison == returns true, the equals() method might return true.
22. x = 0; if (x1.hashCode() != x2.hashCode() ) x = x + 1; if (x3.equals(x4) ) x = x + 10; if (!x5.equals(x6) ) x = x + 100; if (x7.hashCode() == x8.hashCode() ) x = x + 1000; System.out.println("x = " + x); and assuming that the equals() and hashCode() methods are properly implemented, if the output is "x = 1111", which of the following statements will always be true?
23. Which of the following are true statements? The Iterator interface declares only three methods: hasNext, next and remove. The ListIterator interface extends both the List and Iterator interfaces. The ListIterator interface provides forward and backward iteration capabilities. The ListIterator interface provides the ability to modify the List during iteration. The ListIterator interface provides the ability to determine its position in the List.
24. Which statement is true for the class java.util.ArrayList?
25. Suppose that you would like to create an instance of a new Map that has an iteration order that is the same as the iteration order of an existing instance of a Map. Which concrete implementation of the Map interface should be used for the new instance?