Array:

• Creating : int [][] a1= new int [3][3];
• Size/length: a1.length
• Sorting
• Arrays to list:

String:

• toLowerCase()
• toUpperCase()
• replace(‘x’ , ‘y’) replaces all appearances of ‘x’ with ‘y’
• trim() removes the whitespaces at the beginning and at the end
• equals() returns ‘true’ if strings are equal
• equalsIgnoreCase() returns ‘true’ if strings are equal, irrespective of case of characters
• length()
• CharAt(n)
• compareTo() returns negative if string1 < string2 ;positive if string1 > string2; zero if string1 = str2
• concat() concatenates two strings
• substring(n) returns substring returning from character n
• substring(n,m) returns a substring between n and ma character.
• toString() creates the string representation of object
• indexOf(‘x’) returns the position of first occurrence of x in the string.
• indexOf(‘x’,n) returns the position of after nth position in string
• ValueOf (Variable) converts the parameter value to string representation

List:

• Creating list

• Adding elements : a1.add(ele);

• Removing elements: a1. remove(index)

                                 a1.removeAll()
  

• Accessing elements: a1.get(index)
• Size/length: a1.size()
• Sorting
• Removing duplictes stackoverflow.com/questions/203984/how-do-i..

  Set<String> set = new HashSet<>(yourList);
  yourList.clear();
  yourList.addAll(set);
  Of course, this destroys the ordering of the elements in the ArrayList.
  

useful links: stackoverflow.com/questions/24796273/incomp..

HashMap:

• Creating list
• Acessing elements

  map.put(key,value);
  value =  map.get(key) ;
  if( HashMap. containsKey(key)){}
  

• Removing elements

• for (Map.Entry mapElement : hm.entrySet()) { 
            String key = (String)mapElement.getKey(); 
  
            // Add some bonus marks 
            // to all the students and print it 
            int value = ((int)mapElement.getValue() + 10); 
  
            System.out.println(key + " : " + value); 
        }
  

• Sorting -

Priority Queue:

• What is the below initialization ? PriorityQueue<Integer> heap = new PriorityQueue<Integer>((n1, n2) -> n1 - n2); Ans: The constructor accepts a Comparator<? super E> comparator. Basically the statement (n1, n2) -> n1 - n2 is just a shorthand for

Comparator<Integer> result = new Comparator<Integer>() {
        @Override
        public int compare(Integer n1, Integer n2){
            return n1.compareTo(n2);
        }
    };
PriorityQueue<Integer> heap = new PriorityQueue<Integer>(result);

More info :stackoverflow.com/questions/58714930/priori.. PriorityQueue<Integer> minHeap = new PriorityQueue<Integer>(); is equivalent to PriorityQueue<Integer> heap = new PriorityQueue<Integer>((n1, n2) -> n1 - n2);

(Yet to update)

HashSet:

• Creating list
• Acessing elements
• Removing elements
• Printing elements
• Sorting -

TreeSet:

• Creating list
• Acessing elements
• Removing elements
• Printing elements
• Sorting -