Java Multiple Choice Questions & Answers – A Door to Success

Iterator returned by Hashtable on key, value and entry are?

Iterator returned by ConcurrentHashMap on key, value and entry is?

Iterator returned by LinkedHashMap on key, value and entry is?

Iterator returned by TreeMap on key, value and entry is?

Iterator returned by ConcurrentSkipListMap on key, value and entry is?

Which Set implementation is sorted and synchronized?

TreeMap –

What will be the output of the following code –
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

public class MyClass
{
public static void main(String args[])
{
Map<Integer,String> hashMap = new HashMap<Integer,String>();
hashMap.put(11,”a”);
Collections.unmodifiableMap(hashMap);
hashMap.put(12,”b”);
System.out.println(hashMap);
}
}

What will be the output of the following code –
import java. util.Hashtable;
import java. util.Map;
public class hashTableBlog {
public static void main (String args[])
{
Map<Integer,String> hashtable = new Hashtable<Integer,String>();
hashtable.put(11,”a”);
hashtable.put(null,”c”);
hashtable.put(null,null);

System.out.println(hashtable.size());
System.out.println(hashtable);
}
}

What will be the output of the following code –
import java. util.HashMap;

class newEmployee
{
private String name;
public newEmployee (String name)
{
this.name = name;
}
@Override
public int hashCode()
{
return 1;
}
}

class EmployeeClass
{
public static void main(String args[])
{
HashMap hm=new HashMap();
hm.put(new newEmployee(“a”),”emp1″);
hm.put(new newEmployee(“b”),”emp2″);
hm.put(new newEmployee(“a”),”emp1 overridden”);

System.out.println(hm.size());
System.out.println(hm.get(new newEmployee(“a”)));
}

}

What will be the output of the following code –
import java. util.HashMap;

class newEmployee
{
private String name;
public newEmployee (String name)
{
this.name = name;
}
@Override
public int hashCode()
{
return 1;
}
}

class EmployeeClass
{
public static void main(String args[])
{
HashMap<newEmployee,String> hm=new HashMap<newEmployee,String>();
hm.put(new newEmployee(“a”),”emp1″);
hm.put(new newEmployee(“b”),”emp2″);
hm.put(new newEmployee(“a”),”emp1 overridden”);

System.out.println(hm.size());
System.out.println(hm.get(new newEmployee(“a”)));
}

}

What will be the output of the following code –
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.PriorityQueue;

public class MyClass
{
public static void main(String args[])
{
PriorityQueue<Integer> q = new PriorityQueue<Integer>();
q.add(1);
q.add(2);
q.add(3);
System.out.println(q.poll());
System.out.println(q.offer(4));
q.add(1);
q.remove(2);
System.out.println(q.peek());
System.out.println(q);
}
}

Which Map is synchronized?

concurrentSkipListMap permits

Which of these helps insert elements at a specific position in a collection?

Complexity of ArrayList get method

Which of these is sorted by default

Which of these maintains insertion order?

Which maintains insertion order?