String and its Functions

            Strings, which are widely used in Java programming, are a sequence of characters.

The Java platform provides the String class to create and manipulate strings.

Creating Strings

The most direct way to create a string is to write −

String greeting = "Hello world!";

Whenever it encounters a string literal in your code, the compiler creates a String object with its value in this case, "Hello world!'.

String Length

Methods used to obtain information about an object are known as accessor methods. One accessor method that you can use with strings is the length() method, which returns the number of characters contained in the string object.

The following program is an example of length(), method String class.

Example

public class StringDemo {

   public static void main(String args[]) {
      String palindrome = "Dot saw I was Tod";
      int len = palindrome.length();
      System.out.println( "String Length is : " + len );
   }
}

This will produce the following result −

Output

String Length is : 17

Concatenating Strings

The String class includes a method for concatenating two strings −

string1.concat(string2);

This returns a new string that is string1 with string2 added to it at the end. You can also use the concat() method with string literals, as in −

"My name is ".concat("Zara");

Strings are more commonly concatenated with the + operator, as in −

"Hello," + " world" + "!"

which results in −

"Hello, world!"

Let us look at the following example −

Example

public class StringDemo {

   public static void main(String args[]) {
      String string1 = "saw I was ";
      System.out.println("Dot " + string1 + "Tod");
   }
}

This will produce the following result −

Output

Dot saw I was Tod

Creating Format Strings

You have printf() and format() methods to print output with formatted numbers. The String class has an equivalent class method, format(), that returns a String object rather than a PrintStream object.

Using String's static format() method allows you to create a formatted string that you can reuse, as opposed to a one-time print statement. For example, instead of −

Example

System.out.printf("The value of the float variable is " +
                  "%f, while the value of the integer " +
                  "variable is %d, and the string " +
                  "is %s", floatVar, intVar, stringVar);

You can write −

String fs;
fs = String.format("The value of the float variable is " +
                   "%f, while the value of the integer " +
                   "variable is %d, and the string " +
                   "is %s", floatVar, intVar, stringVar);
System.out.println(fs);

String charAt()

Description

This method returns the character located at the String's specified index. The string indexes start from zero.

Syntax

Here is the syntax of this method −

public char charAt(int index)

Parameters

Here is the detail of parameters −

• index − Index of the character to be returned.

Return Value

• This method returns a char at the specified index.

Example

public class Test {

   public static void main(String args[]) {
      String s = "Strings are immutable";
      char result = s.charAt(8);
      System.out.println(result);
   }
}

This will produce the following result −

Output

a

String Methods

Here is the list of methods supported by String class −

Sr.No.	Method & Description
1	char charAt(int index) Returns the character at the specified index.
2	int compareTo(Object o) Compares this String to another Object.
3	int compareTo(String anotherString) Compares two strings lexicographically.
4	int compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case differences.
5	String concat(String str) Concatenates the specified string to the end of this string.
6	boolean contentEquals(StringBuffer sb) Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
7	static String copyValueOf(char[] data) Returns a String that represents the character sequence in the array specified.
8	static String copyValueOf(char[] data, int offset, int count) Returns a String that represents the character sequence in the array specified.
9	boolean endsWith(String suffix) Tests if this string ends with the specified suffix.
10	boolean equals(Object anObject) Compares this string to the specified object.
11	boolean equalsIgnoreCase(String anotherString) Compares this String to another String, ignoring case considerations.
12	byte getBytes() Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
13	byte[] getBytes(String charsetName) Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
14	void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Copies characters from this string into the destination character array.
15	int hashCode() Returns a hash code for this string.
16	int length() Returns the length of this string.
17	int indexOf(String str) Returns the index within this string of the first occurrence of the specified substring.
18	int indexOf(String str, int fromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
19	String intern() Returns a canonical representation for the string object.
20	String toString() This object (which is already a string!) is itself returned.
21	int lastIndexOf(String str) Returns the index within this string of the rightmost occurrence of the specified substring.
22	int lastIndexOf(String str, int fromIndex) Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
23	boolean startsWith(String prefix) Tests if this string starts with the specified prefix.
24	boolean startsWith(String prefix, int toffset) Tests if this string starts with the specified prefix beginning a specified index.
25	String replace(char oldChar, char newChar) Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
26	String replaceAll(String regex, String replacement Replaces each substring of this string that matches the given regular expression with the given replacement.
27	String replaceFirst(String regex, String replacement) Replaces the first substring of this string that matches the given regular expression with the given replacement.
28	String[] split(String regex) Splits this string around matches of the given regular expression.
29	String[] split(String regex, int limit) Splits this string around matches of the given regular expression.
30	String substring(int beginIndex) Returns a new string that is a substring of this string.
31	String substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string.
32	String toLowerCase() Converts all of the characters in this String to lower case using the rules of the default locale.
33	String toUpperCase() Converts all of the characters in this String to upper case using the rules of the default locale.
34	String trim() Returns a copy of the string, with leading and trailing whitespace omitted.
35	static String valueOf(primitive data type x) Returns the string representation of the passed data type argument.