Sorting in Collection

Sorting in Collection

• Sorting is any process of arranging items systematically
  
• It has distinct meanings: ordering: arranging items in a sequence ordered by some criterion, categorizing: grouping items with similar properties.
• There are two types of sorting: Ascending and Descending.
  
• Types of Sorting Techniques
• Bubble Sort.
  
• Selection Sort.
  
• Merge Sort.
  
• Insertion Sort.
  
• Quick Sort.
  
• Heap Sort.
  
• We can sort the elements of:
• String objects
• Wrapper class objects
• Collections class provides static methods for sorting the elements of a collection. 
• If collection elements are of a Set type, we can use TreeSet. 

• Collections class provides methods for sorting the elements of List type elements.

• public void sort(List list): is used to sort the elements of List. List elements must be of the Comparable type.

Example to sort string objects.

ArrayList al=new ArrayList();  
al.add("One");
al.add("Second");
al.add("Third");
al.add("Four");
Collections.sort(al);
Iterator itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}

Example to sort string objects in reverse order

ArrayList al=new ArrayList();  
al.add("One");
al.add("Second");
al.add("Third");
al.add("Four"); 
       
Collections.sort(al,Collections.reverseOrder());  

Iterator i=al.iterator();
while(i.hasNext())
{
 System.out.println(i.next());
}

Example to sort Wrapper class objects

ArrayList al=new ArrayList();
al.add(Integer.valueOf(201));
al.add(Integer.valueOf(101));
//internally will be converted into objects as Integer.valueOf(230)
al.add(230);

Collections.sort(al);  

Iterator itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}