6-Collections operational APIs in common

Sorting: 

• Already sorted Collections are as below. 
• TreeSet
• TreeMap

However for the rest, a comparator needs to be implemented in 3 following ways:

• sort() method for sorting List:
• List l = new ArrayList(Arrays.asList(3, 5, 4, 2, 3, 2, 1, 3));
• Collections.sort(l); //increasing order
• System.out.println("Increasing order:"+l);
• O/p: Increasing order: [1, 2, 2, 3, 3, 3, 4, 5]
• .
• However, The element’s class must implement Comparable interface. This is mandatory since this version of sort() uses element’s compareTo() method to compare them. Otherwise a ClassCastException will be thrown.

• custom Sort method for sorting List:Steps to create custom Comparator are below:
• create a custom comparator class that implements Comparator interface, and implement its compare() method as below:
• class IntegerComparator implements Comparator {
•     public int compare(Object o1, Object o2) {
•       return (Integer)o2 - (Integer)o1;
•     }
• }
• Note that the Object that is compared(Integer in this case) needs to implement Comparable interface in order to be use a comparator(IntegerComparator  in this case) for comparison.
• This customComparator(IntegerComparator) then used as in below code:
• Collections.sort(l, new IntegerComparator());//decreasing order
• System.out.println("Decreasing order\n"+l);
• Using unnamed Comparator class(within sort() call)
• Collections.sort(l, new Comparator() {
• public int compare(Object o1, Object o2) {
• return (Integer)o2 - (Integer)o1;
• }}
• ); //decreasing order

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Shuffling: 

• The opposite of sort is shuffle which arranges list elements arbitrarily.
• Two versions of shuffle() are :
1. One operates on a List using a default source of randomness.
• Collections.shuffle(l);
2. Another requires a Random object to be specified explicitly.
• Collections.shuffle(l, new Random());

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Manipulation: 

• Reversing : Collections.reverse(list);
• Swapping : swaps elements of two specified positions of a specified list
• Collections.swap(list,2, 4);
• Copying : Copy all the elements on lists1 into list2
• Collections.copy(list1, list2);
• Filling : fill all elements of list1 with "0", wrt to example below
• Collections.fill(list,0);
• Adding: Collections.addAll(l1, -1, -2, -3);//Adds three integers to the list l1.

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Search: 

• binarySearch(): It is common to use sort() method to sort the List before a call to binarySearch().
• Collections.sort(list); //list=[1, 2, 2, 3, 3, 3, 4, 5]
• int in = Collections.binarySearch(l, 4); //in = 6
• in = Collections.binarySearch(list, 2); //in = 1
• in = Collections.binarySearch(list, 3); //in = 3
• For unsuccessful search, it returns a value (-(insertion point) - 1),
• in = Collections.binarySearch(list, 0); //in = -1

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min()/max(): 

• int min = (int)Collections.min(list); //min = 0
• int max = (int)Collections.max(list); //max = 6

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frequency(): 

• int fre = Collections.frequency(list,2); //fre = 2
• fre = Collections.frequency(list,3); //fre = 3

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