Strings

String is a sequence of characters. But, many other languages that implement strings as character arrays, Java implements strings as objects of type String. Implementing strings as built-in objects allows Java to provide a full complement of features that make string handling convenient.

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

Creating Strings

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!'.

As with any other object, you can be create String object by using the new keyword and a constructor. The String class has 11 constructors that allow you to provide the initial value of the string using different sources, such as an array of characters. Example


public class StringDemo {

   public static void main(String args[]) {
      char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
      String helloString = new String(helloArray);  
      System.out.println( helloString );
   }
}

This will produce the following result −


Output
hello.

The string class is irreversible, so that once it can be made to a string object. If the string of characters is required to make many modifications, then you should use string buffer and string builder classes.

String Length

The length of a string is the number of characters in which it is included. To achieve this value, call the length () method.


int length( )

The following fragment prints "3"?, since there are three characters in the string s:


char chars[] = { 'a', 'b', 'c' };
String s = new String(chars); 
System.out.println(s.length());

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

Example


public class StringExample {

   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 following result −


Output
String Length is : 17 

Concatenating Strings

The String class is 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's consider following 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 −


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 Methods

Here is the list of methods supported by String class −

  • char charAt(int index) Returns the character at the specified index.
  • int compareTo(Object o) Compares this String to another Object.
  • int compareTo(String anotherString) Compares two strings lexicographically.
  • int compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case differences.
  • String concat(String str) Concatenates the specified string to the end of this string.
  • boolean contentEquals(StringBuffer sb) Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
  • static String copyValueOf(char[] data) Returns a String that represents the character sequence in the array specified.
  • static String copyValueOf(char[] data, int offset, int count) Returns a String that represents the character sequence in the array specified.
  • boolean endsWith(String suffix) Tests if this string ends with the specified suffix.
  • boolean equals(Object anObject) Compares this string to the specified object.
  • boolean equalsIgnoreCase(String anotherString) Compares this String to another String, ignoring case considerations.
  • byte getBytes() Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
  • byte[] getBytes(String charsetName) Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
  • void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Copies characters from this string into the destination character array.
  • int hashCode() Returns a hash code for this string.
  • int indexOf(int ch) Returns the index within this string of the first occurrence of the specified character
  • int indexOf(int ch, int fromIndex) Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
  • int indexOf(String str) Returns the index within this string of the first occurrence of the specified substring.
  • 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.
  • String intern() Returns a canonical representation for the string object.
  • int lastIndexOf(int ch) Returns the index within this string of the last occurrence of the specified character.
  • int lastIndexOf(int ch, int fromIndex) Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
  • int lastIndexOf(String str)Returns the index within this string of the rightmost occurrence of the specified substring.
  • 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.
  • int length() Returns the length of this string.
  • boolean matches(String regex) Tells whether or not this string matches the given regular expression.
  • boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len) Tests if two string regions are equal.
  • boolean regionMatches(int toffset, String other, int ooffset, int len) Tests if two string regions are equal.
  • String replace(char oldChar, char newChar) Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
  • String replaceAll(String regex, String replacement ) Replaces each substring of this string that matches the given regular expression with the given replacement.
  • String replaceFirst(String regex, String replacement) Replaces the first substring of this string that matches the given regular expression with the given replacement.
  • String[] split(String regex) Splits this string around matches of the given regular expression.
  • String[] split(String regex, int limit) Splits this string around matches of the given regular expression.
  • boolean startsWith(String prefix) Tests if this string starts with the specified prefix.
  • boolean startsWith(String prefix, int toffset) Tests if this string starts with the specified prefix beginning a specified index.
  • CharSequence subSequence(int beginIndex, int endIndex) Returns a new character sequence that is a subsequence of this sequence.
  • String substring(int beginIndex) Returns a new string that is a substring of this string.
  • String substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string.
  • char[] toCharArray() Converts this string to a new character array.
  • String toLowerCase() Converts all of the characters in this String to lower case using the rules of the default locale.
  • String toLowerCase(Locale locale) Converts all of the characters in this String to lower case using the rules of the given Locale.
  • String toString() This object (which is already a string!) is itself returned.
  • String toUpperCase() Converts all of the characters in this String to upper case using the rules of the default locale.
  • String toUpperCase(Locale locale) Converts all of the characters in this String to upper case using the rules of the given Locale.
  • String trim() Returns a copy of the string, with leading and trailing whitespace omitted.
  • static String valueOf(primitive data type x) Returns the string representation of the passed data type argument.

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