You can concatenate two Strings using the concat() method.ExampleLive Demopublic class ConcatinatedStrings {    public static void main(String args[]) {             String str1 = new String("Tutorials");       String str2 = new String( "Point");       String res = str1.concat(str2);       System.out.println(res);    } }OutputTutorialsPoint

String class is immutable once you create an object of string you can modify its data.The StringBuffer class is immutable, once you create a StringBuffer object you can change/modify the contents of it.This class provides various methods to manipulate its data such as append(), delete(), insert() etc.

The toString() method returns the current object in String format.ExampleLive Demopublic class Test { public static void main(String args[]) { Test obj = new Test(); System.out.println(obj.toString()); System.out.println("Hello"); } }OutputTest@2a139a55 Hello

When the String literal used to create String, JVM initially checks weather String with the same value in the String constant pool, if available it creates another reference to it else it creates a new object and stores it in the String constant pool.In case of an object, each time you instantiate the class a new object is created given value irrespective of the contents of the String constant pool.

The StringBuffer and StringBuilder classes are used when there is a necessity to make a lot of modifications to Strings of characters.Unlike Strings, objects of type StringBuffer and String builder can be modified over and over again without leaving behind a lot of new unused objects.The StringBuilder class was introduced as of Java 5 and the main difference between the StringBuffer and StringBuilder is that StringBuilder’s methods are not thread safe (not synchronized).It is recommended to use StringBuilder whenever possible because it is faster than StringBuffer. However, if the thread safety is necessary, the best option is StringBuffer objects.Read More

When you store a String asString str1 = "Hello";directly, then JVM creates a String object with the given value in a separate block of memory known as String constant pool.And whenever we try to create another String asString str2 = "Hello";JVM verifies whether any String object with the same value exists in the String constant pool, if so, instead of creating a new object JVM assigns the reference of the existing object to the new variable.And when we store String asString str = new String("Hello");using the new keyword, a new object with the given value is created irrespective of the ... Read More

You can create a String by − Step 1 − Assigning a string value wrapped in " " to a String type variable. String message = "Hello Welcome to Tutorialspoint"; Step 2 − Creating an object of the String class using the new keyword by passing the string value as a parameter of its constructor. String message = new String ("Hello Welcome to Tutorialspoint"); Step 3 − Passing a character array to the String constructor. char arr[] = {'H','e','l','l','o'}; String message = new String(arr);

In Java, immutable objects are those whose data can’t be changed or modified (once modified). String class is immutable i.e. once we create a String object its data cannot be modified.

Java provides the java.util.regex package for pattern matching with regular expressions.

transient: An instance variable is marked transient to indicate the JVM to skip the particular variable when serializing the object containing it.  This modifier is included in the statement that creates the variable, preceding the class or data type of the variable.Examplepublic transient int limit = 55;   // will not persist public int b;   // will persistvolatile: The volatile modifier is used to let the JVM know that a thread accessing the variable must always merge its own private copy of the variable with the master copy in the memory.Accessing a volatile variable synchronizes all the cached copied ... Read More