String

● is Class which contains sequence of characters

● is the only Non-Primitive Data Type that can be instantiated using Literal (String Literal)

● can also be instantiated using String Class

Declare String

//DECLARE USING STRING LITERAL.

String text = ""; //Empty string.text.length()=0,text.equals("")==true

text = "Hello World"; //Creates String Object with constant text "text".

text = "First line. \n Second line."; //Using escape character '\': \" \t \n \\

text = "Start" + "End"; //Connecting Strings.

//DECLARE USING STRING CONSTRUCTOR.

String text = null; //Calling any function on text throws Exception

text = new String(); //Empty string.

text = new String("text"); //Creates String Object from String Literal

text = new String(new byte[] {'J','o','h','n'}); //Creates String Object from byte array.

//DECLARE USING STRING METHODS.

String text = String.copyTextOf(new char[] {'J','o','h','n'}, 1, 2); //From index 1 take 2: "oh"

text = String.textOf (65 );

text = String.valueOf(65.0);

Modify String

String text = "012345 \n";

String modified = text.toUpperCase (); //Converts all characters to upper case.

modified = text.toLowerCase (); //Converts all characters to lower case.

modified = text.replace ('3', 'A' ); //Replace ALL occurrences of char '3' with 'A'.

modified = text.replaceFirst("23","AB"); //Replace FIRST occurrences of regex "23" with "AB".

modified = text.replaceAll ("23","AB"); //Replace ALL occurrences of regex "23" with "AB".

modified = text.replaceAll ("[\n\r]",""); //Remove all \n and \r characters.

Get Substring

String text = "012345";

String substr = text.substring (2); //Take substring from index 2 till the end. Result is "2345"

substr = text.substring (2,5); //Take substring from index 2 till 5-1=4. Result is "234".

substr = text.trim (); //Erases leading and trailing whitespaces: \t \n

Split String

String text = "zero<->one<->two<->three";

String[] tokens = text.split("<->" ); //Split string around "<->" regex. Gives tokens[0]="one";

tokens = text.split("<->",3); //Create maximum 3 tokens. Gives tokens[2]="two<->three";

tokens = text.split("[135]"); //Split string around 1,3 and 5.

tokens = text.split("/" ); //Split string around '/'.

tokens = text.split("\\." ); //Split string around '.'.

tokens = text.split("\\\\" ); //Split string around '\'.

tokens = "" .split(";" ); //One token is returned resulting in tokens.length=1.

tokens = ";" .split(";" ); //No tokens are returned resulting in tokens.length=0.