Java - Basics

Lets learn the basics of Java collections with code samples

1. Arrays
   
   Most of the time we only need one property of an array that is its length below is a sample code
   
   int[] intArray = new int[10];
   int arrayLen = intArray.length;
   
   
2. Chars
   Characters data type is another common data type used in programming. For example to convert a character to an integer
   
   

   int intValue = Character.getNumericValue(example.charAt(0));
   
   

3. Strings
   Strings have several other useful properties unlike arrays like, length, convert to integer to string, to char array to name a few. Below are a set of examples.
   
   

   String example = "You are almost there";
   
   //Find the length of string 
   System.out.println("String Length is: " + example.length());
   
   //Convert string to Char array 
   char[] charArr = example.toCharArray();
   
   //Access a character at index i 
   char charAtIndex = example.charAt(0);
   
   //Get each character's ascii 
   int asciiValue = example.codePointAt(0);
   
   //Get access to the ASCII value of the character before index i 
   int k = example.codePointBefore(1);
   
   //To compare two strings, it return 0 if they are same,
   // else returns a negative number if argument is lexicographically greater// 
   return a positive number if the argument is lexicographically lesser than the parent string
   int compare = example.compareTo("You are almost there");
   
   //Same as compareTo except it ignores case 
   int ignoreCaseCompare = example.compareToIgnoreCase("you are almost there");
   
   //To concatenate a string to the existing one, it resturns a String 
   String concatenated = example.concat(" on your way to Google");
   
   //To compare another string for equality. 
   boolean bool = example.equals("You are almost there");
   
   //To find the starting index of another string within a String 
   int index = example.indexOf("almost");
   
   

4. StringBuilder
   
   String is immutable, if you try to alter their values, another object gets created, whereas
   StringBuffer and StringBuilder are mutable so they can change their values. Thread-
   
   Safety Difference: The difference between StringBuffer and StringBuilder is that StringBuffer is thread-safe.
   
   Now lets see most frequently used functions of a StringBuilder class
5. Stack
   Stack uses LIFO principle and is a very useful technique for any programming task.
   
   

   //Initialize a Stack 
   Stack stack = new Stack();

   //Push an element into a Stack

   stack.push(1);
   //Pop an element from a Stack, it returns a
   

   int k = stack.pop(); 
   
   //Peek an element from top of the stack
   stack.peek();
   //Check if the stack is empty
   stack.empty();
   

6. Queue
   
   

   Queue q = new LinkedList();
   //To add an element in Queue
   q.add(1);
   //To remove an element in Queue
   q.remove()
   
   
   
   

7. Priority Queue
8. List
   
   List tempList = new ArrayList()
   int length = tempList.size();
   
9. Array List
10. Hash Map
    
    

    HashMap hashMap = new HashMap();
    
    //To get put elements in HashMap
    hashMap.put(1,"Arun");
    hashMap.put(2,"Amma and Nanna");
    hashMap.put(3,"Theertha");
    
    //To get size of hashMap
    System.out.println("Hash Map Size " + hashMap.size());

11. Hash Set

         HashSet hSet = new HashSet();

     hSet.add(1);
     hSet.add(2);
     hSet.add(3);

       

     //To get size of hashMap

         if(hSet.contains(1))
          System.out.println("Hash Map Contains 1");