Objects and Collections Questions

• Which Java class inherits its equals() and hashCode() directly from java.lang.Object (i.e., does not override them)?
• Which Java collection lets you associate elements with keys while iterating in insertion (FIFO) order?
• Java — Which interface does java.util.Hashtable implement?
• Java — What is the numerical range of the char data type?
• Java — Store elements with no duplicates and natural order. Which interface provides this capability?
• Java — Which Map implementation maintains iteration order of an existing Map?
• Java — Which collection class allows resizing, provides indexed access, but is not synchronized?
• Java — What line of code should replace the missing statement to compile this program? 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"); } }
• Java — Which interface provides capability to store objects using key-value pairs?
• Java — Which of the following are Java reserved words? (run, import, default, implement)
• Java — Which collection class allows key-value associations and provides synchronization?
• Java — Which is a valid declaration of a float value?
• Java TreeSet iteration order and duplicate handling: what sequence is printed? TreeSet map = new TreeSet(); map.add("one"); map.add("two"); map.add("three"); map.add("four"); map.add("one"); // duplicate Iterator it = map.iterator(); while (it.hasNext()) { System.out.print(it.next() + " "); }
• Static array reference default value vs element access: what happens when printing x[0]? public class Test { private static int[] x; // reference not initialized → null public static void main(String[] args) { System.out.println(x[0]); } }
• Which interfaces does Vector.elements() return, and how do instanceof tests evaluate? 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); } }
• Packages, access modifiers, and top-level classes: will this code compile? 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 } }
• Default values in a newly allocated float array: what exactly prints for f[0]? public class Test { private static float[] f = new float[2]; public static void main (String[] args) { System.out.println("f[0] = " + f[0]); } }
• Which interfaces does ArrayList.iterator() implement? Evaluate the instanceof results. 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); } }
• Using NULL vs null in Java: what does this program do? public class Test { public static void main (String args[]) { String str = NULL; System.out.println(str); } }
• In Java command-line arguments, what is printed by this program when executed as shown? 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 } } Invocation: > java Test red green blue