1. To convert arrays to list use Arrays.asList() method

List l = Arrays.asList(arr);

note

The type of array must be a Wrapper Class(Integer,FLoat, etc) in case of primitive data types(int,float,etc) , i.e you can’tpass int a[] but you can pass Integer a[]. If you pass int a[],this function will return a List <int a[]> and not List<Integer> , as “autoboxing” doesn’t happens in this case and int a[] is itself identified as an object and a List of intarray is returned, instead of list of integers , which will give error in various Collection functions

2. Initialize ArrayList

ArrayList<datatype> al = new ArrayList<datatype>();

List<datatype> al = new ArrayList<datatype>();

3. Set - Set don't allow duplicate elements

• Initialize
• Set is a unordered collection of unique data, data is stored and retrieved in random order.

Set<datatype> set = new HashSet<datatype>();

• LinkedHashSet - ordered collection of set, data is stored and retrieved in the same order
  LinkedHashSet<datatype> t = new LinkedHashSet<datatype>();
• TreeSet (sorted Set) - all the elements are sorted in ascending order
  TreeSet<datatype> t = new TreeSet<datatype>();

  // To get the highest element

  t.pollLast();

4. Initialize Stack

Stack<datatype> stack = new Stack<datatype>();

• Stack operations
  • push() - push element to the stack
    stack.push(element);
  • pop() - pop top element from the stack and returns the element
    datatype n = stack.pop();
  • peek() - returns top element of the stack without removing
    datatype n = stack.peek();
  • isEmpty() - is used to check if a stack is empty or not, returns true/false
    stack.isEmpty();

5. Iterate a List (in A Loop)

• First create a iterator for the list
  Iterator i = list.listIterator();
• Iterate through list using hasNext() check condition, it returns boolean if the next element is present from the position of the iterator i
  i.hasNext();
• Get the element of the list, returns the next element of the list until the hasNext condition fails
  i.next();