public class JavaBuff          // Class name                  
    {                                                                     
     public JavaBuff()            // Default Constructor   
       { } 
    public void JavaBuff()   //Valid but considered bad coding practice
      {}
} 

 Points to ponder :

Overloading a Constructor

public class JavaBuff          // Class name                
{                                                                    
    public JavaBuff()            //Default Constructor 1  
      { }  
    public  JavaBuff(int a , int b)   // Overloaded Constructor 2  
      { }
    public  JavaBuff(String x , String y)   // Overloaded Constructor 3  
      { }
 }

Concurrent Modification

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class FailFastExample
{
    
    
    public static void main(String[] args)
    {
        Map mapExample = new HashMap();
        mapExample.put("key1", "value1");
        mapExample.put("key2", "value2");
        mapExample.put("key3","value3");
        
        Iterator iterator = mapExample.keySet().iterator();
        
        while (iterator.hasNext())
        {
            System.out.println(mapExample.get(iterator.next()));
            mapExample.put("key4", "value4");
        }
        
    }
    
}

import java.util.concurrent.ConcurrentHashMap;
import java.util.Iterator;


public class FailSafeExample
{
    
    
    public static void main(String[] args)
    {
        ConcurrentHashMap mapExample = 
                               new ConcurrentHashMap();
        mapExample.put("key1", "value1");
        mapExample.put("key2", "value2");
        mapExample.put("key3","value3");
        
        Iterator iterator = mapExample.keySet().iterator();
        
        while (iterator.hasNext())
        {
            System.out.println(mapExample.get(iterator.next()));
            mapExample.put("key4", "value4");
        }
        
    }
    
}

Q #1) What is the Iteration in Java?

• Enumerators
• Iterators
• ListIterators

• boolean hasNext() - Returns true if the iteration has more elements.
• E next() - Returns the next element in the iteration.
• void remove() - Removes from the underlying collection the last element returned by the iterator (optional operation).

java.util.Scanner s = new java.util.Scanner(new java.io.File("test.txt"));
while(s.hasNext()) { 
 System.out.println(s.next());
}

• Considerable improvement in method names.
• You can remove method elements from the collection that is being traversed using an iterator.

import java.util.*;
public class ArrayListIteratorTest {
 public static void main(String[] args) {
  ArrayList al1 = new ArrayList();
  al1.add("one");al1.add("two");
  al1.add("three");
  Iterator i = al1.iterator();
  String l;
  while(i.hasNext()) {
   l = (String)i.next();
   System.out.println(l);
  }
 }
}

1. void clear(): It removes all the key and value pairs from the specified Map.
2. Object clone(): It returns a copy of all the mappings of a map and used for cloning them into another map.
3. boolean containsKey(Object key): It is a boolean function which returns true or false based on whether the specified key is found in the map.
4. boolean containsValue(Object Value): Similar to containsKey() method, however it looks for the specified value instead of key.
5. Value get(Object key): It returns the value for the specified key.
6. boolean isEmpty(): It checks whether the map is empty. If there are no key-value mapping present in the map then this function returns true else false.
7. Set keySet(): It returns the Set of the keys fetched from the map.
8. value put(Key k, Value v): Inserts key value mapping into the map. Used in the above example.
9. int size(): Returns the size of the map – Number of key-value mappings.
10. Collection values(): It returns a collection of values of map.
11. Value remove(Object key): It removes the key-value pair for the specified key. Used in the above example.
12. void putAll(Map m): Copies all the elements of a map to the another specified map.

1. Sort the array or list of objects, but NOT in natural order.
2. Sort the array or list of objects where we can not modify the object’s source code to implement Comparable interface.
3. Sort same list or array of objects on different fields.
4. Using group by sort on list or array of objects on different fields.

Employee.java

SortByName.java

Output: