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String is most used java class in any java project. Java treated String as special class. Lets see, what so special in String. String Basics String is group of characters. char[] chrs = {'i',' ','a','m',' ','h','e','r','o','.'}; String str = new String(chrs); System.out.println(str); /* Output: i am hero. */ String is an immutable class. Immutable class:  A java class which object can not be modified if once created. Because String class is immutable, String is final in nature, its mean you can not modify string object once you created. Default value of string is null. Simplest way to initialize String is //object created in String Literal Pool String str = "hello world"; Above example known as String literal, All string literals in Java programs, such as "hello world", are object of String class. Another way to create String object is //object created in Heap m

Assume we have 5 array of integer type and we want to add all numbers of array. 1st way ( Sequential Way ) We can pick array one by one and add all numbers and give the result. In this way only one thread (main thread) will execute the program. 2nd way ( Multithreaded Way ) In Multithreaded way, we can create 5 thread and assign an array to each thread to add all the numbers of array. All 5 thread will run parallel and give result 5 times faster than 1st way. What is Thread & Multithreading? A process may contain sub processes which execute parallel and use same resource of main process these sub processes are threads and whole phenomena called Multithreading . How to implement thread in Java? Java thread is sub process of process. In java, Thread class use to achieve multithreading in program. Initialize Thread There is two way to initialize and run thread in java. By extending Thread class By implementing Runnable interface By extending Thre

Java I/O Stream Input Stream: Taking input data from other source in your program. Output Stream: Your program giving some data to other source. Note: Other source can be another java program, console, file or any other program. Task 1st: Take input character from console and print it on console. Java input output classes belongs to java.io package and by default each and every class in java have java.lang package. java.lang package contains System class, which we use for print something on console like System.out.println("Hello World"); if you open System class src code, you will find system class has a PrintStream type variable with name out and this PrintStream class belongs to java.io package have method println(String arg) , which print passed argument in print method on console. I/O variables of System Class: System.out: use for giving output to console. Type: PrintStream System.in: taking input from console. Type: InputStream import java.io.IOEx

Collection framework is use for storing data in program. Collection framework contains most of data structure like LinkedList, Set, HashMap etc already implemented for you to direct use in program and also gives you flexibility to write own kind of data structure. Java collections framework data structure: Lists: Contains list of objects. Java provides 3 type of ready to use list. ArrayList Vector LinkedList Sets: Contains unique objects, does not allow dublicates. Java provides 3 type of sets, these are HashSet LinkedHashSet TreeSet Maps: Contain key:value data structure, value only access by key. Java provides 4 type of Map. HashMap Hashtable LinkedHashMap TreeMap Queues: Perform FIFO (first in first out) PriorityQueue Java Collection Interface And Collections Util Class Collection is an interface which is implemented by all data structure in java, except Map. Maps (HashMap, LinkedHashMap, Hashtable, TreeMap) are not define by Collection interface, th

Exceptions are exceptional conditions in program flow. What is the exceptional conditions? You going to read a file. Exceptional condition: File is not found.(FileNotFound Exception) You creating a new file. Exceptional condition: No space in memory for new file, you dont have rights to create a new file in drive. You are performing some operation on object. Exceptional condition: object is null.(NullPointer Exception) Mathematical exceptions like number divide by zero.(ArithmeticException) Array related exception like accessing an index which not in array(ArrayOutOfBound Exception). There are many cases where exception can occurs in your program. For your program runs as you expected,You need to perform exception handling for exceptional conditions but before go to exception handling lets know about Exception in java. public class Test{ void printName(){ System.out.println("Test"); } public static void main(String[] args) { Test test

Java has classes, A class has properties. These properties with values called object or state of object. Now we want to save this state of object into file or database. With java serialization we can convert object state into data stream and this data stream would be save into file system or database or create object replica into another system. Java Serialization Covered Two Process - Serialization : Convert object state into data stream. Deserialization : Convert data stream into object state.  Simple Java Code Example:  import java.io.Serializable; public class Student implements Serializable{ private String name; private int age; public Student(String name, int age) { this.name = name; this.age = age; } public void print() { System.out.println("Name:"+name+" Age:"+age); } } import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputS