Java Collection maps

Which is faster and uses less memory?

• ListEnumeration

• Iterator

• Enumeration

• ListIterator

Which interface does java.util.Hashtable implement?

• Java.util.Map

• Java.util.List

• Java.util.HashTable

• Java.util.Collection

Find the output

public class TreeMapTest {

public static void main(String args[]) {

Map<Integer, String> m = new TreeMap<Integer, String>();

m.put(11, "audi");

m.put(null, null);

m.put(11, "bmw");

m.put(null, "ferrari");

System.out.println(m.size());

System.out.println(m);

}

• Nullpointer exception

• compiler error

• 2

• Null value

public class MyClass {

public static void main(String args[]) {

Map<String, String> hashMap = new HashMap<String, String>();

hashMap.put(new String("a"), "audi");

hashMap.put(new String("a"), "ferrari");

System.out.println(hashMap);

}

}

• a=audi

• a=audi

  a=ferrari

• a=ferrari

• Run time Error

Which of these is synchronized?

• TreeMap

• HashMap

• Hashtable

• All of the above

How can you sort given HashMap on basis of values

• Implement Comparator interface and override its compare method

• It is not possible

• Implement Comparator interface and override its compareTo method

• Implement Comparator interface and override its comparable method

Which of the following statement is not True about Generics in java?

• Generics are features of the Java programming language that allow programmers to write parameterized code.

• With generics, the compiler can not detect violations at compile time, thus eliminating potential bugs.

• Due to the demand of safer code, generics were added to the Java programming language.

• generics allow you to write generic code

• Stronger type checks at compile time

What is a HashMap?

• a bunch of key-value pairs

• a type of ArrayList

• a type of 2D array

• a type of 3D array

How many values can each key in a HashMap be associated with?

• one

• depends how you initialize the HashMap

• unlimited

• trick question--keys aren't associated with values in a HashMap

What do you use to access every member of a HashMap?

• a for loop

• a for-each loop

• an array

• an ArrayList