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17. String.md

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17. String.md

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17. String

  • The String data type is used to store a sequence or array of characters (text). But in Java, a string is an object that represents an array or sequence of characters.
  • The java.lang.String is the class is used for creating a string object.
  • String literals should be enclosed within double-quotes. The difference between a character array and a string is that in the string a special character ‘\0’ is present
  • Strings are immutable. This means that it is not possible to change the values of the characters within a String.
  • String <String_variable_name> = “<sequence_of_strings>"

Two ways of creating string:

  • using string literal String myString = “Hello World”
  • using new keyword String myLine = **new** String(“Hello World!!!”);

String methods:

String word = "Hello world";
// String methods
// character at a given indes
System.out.println(word.charAt(0)); // H
// length of the string
System.out.println(word.length()); // 11
// substring
System.out.println(word.substring(2,7); // llo w
// get index of a character
System.out.println(word.indexOf('l'); // 2
System.out.println(word.indexOf('a'); // -1
System.out.println(word.indexOf("world"); // 6
System.out.println(word.indexOf("mello"); // -1

System.out.println(word.startsWith("hello"); // true

// compareT0 => -ve (smaller) 0 (equal) +ve (greater)
System.out.println(word.compareTo("abc")); // +ve
System.out.println("a".compareTo("b")); // -ve
System.out.println("b".compareTo("b")); // 0

// split operation
String[] arr = "hello there,Bob".split(" "); //["hello","there,Bob"]
// split with multiple delimiters separate with pipe "|" operator
String[] arr1 = "hello there,Bob".split(" |,");// ["hello", "there", "Bob"]

// for using dot (.) as a delimiter. use \\.
String t = "Hello,strings can be fun. They have many uses.";
String[] result = t.split(",| |\\. |\\."); // ["Hello", "strings", "can", "be", "fun", "They", "have", "many", "uses"]

Formatting String.

Specifier Value
%b boolean
%c character
%d decimal integer
%f float
%e number in scientific notation
%s string 
String newStr = String.format("you owe me $%f",200.54f);

System.out.println(newStr);

System.out.printf("you owe me $%.2f",345.44f);