Java Operators

Java Control Statements

Object Oriented Programming

Java Built-in Classes

Java File Handling

Java Error & Exceptions

Java Multithreading

Java Synchronization

Java Networking

Java Collections

Java Interfaces

Java Data Structures

Java Collections Algorithms

Advanced Java

Java Miscellaneous

Java APIs & Frameworks

Java Class References

Java Useful Resources

Java - String Class

Previous
Quiz

Strings, which are widely used in Java programming, are a sequence of characters. In Java programming language, strings are treated as objects.

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!".

As with any other object, you can create String objects 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 to Create Strings in Java

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 );
   }
}

Output

hello.

Note − The String class is immutable, so that once it is created a String object cannot be changed. If there is a necessity to make a lot of modifications to Strings of characters, then you should use String Buffer & String Builder Classes.

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 to Get String Length in Java

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 to Concatenate Strings in Java

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 to Create Formatted Strings in Java

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);

Java String Class Methods

The following are the built-in methods of the String class in Java with their syntaxes and usages −

Sr.No.Method & Description
1char charAt(int index)

This method returns the char value at the specified index.

2int codePointAt(int index)

This method returns the character (Unicode code point) at the specified index.

3int codePointBefore(int index)

This method returns the character (Unicode code point) before the specified index.

4int codePointCount(int beginIndex, int endIndex)

This method returns the number of Unicode code points in the specified text range of this String.

5int compareTo(String anotherString)

This method compares two strings lexicographically.

6int compareToIgnoreCase(String str)

This method compares two strings lexicographically, ignoring case differences.

7String concat(String str)

This method concatenates the specified string to the end of this string.

8boolean contains(CharSequence s)

This method ceturns true if and only if this string contains the specified sequence of char values.

9boolean contentEquals(CharSequence cs)

This method compares this string to the specified CharSequence.

10boolean contentEquals(StringBuffer sb)

This method compares this string to the specified StringBuffer.

11static String copyValueOf(char[] data)

This method returns a String that represents the character sequence in the array specified.

12static String copyValueOf(char[] data, int offset, int count)

This method returns a String that represents the character sequence in the array specified.

13boolean endsWith(String suffix)

This method tests if this string ends with the specified suffix.

14boolean equals(Object anObject)

This method compares this string to the specified object.

15boolean equalsIgnoreCase(String anotherString)

This method compares this String to another String, ignoring case considerations.

16static String format(Locale l, String format, Object... args)

This method returns a formatted string using the specified locale, format string, and arguments.

17static String format(String format, Object... args)

This method returns a formatted string using the specified format string and arguments.

18byte[] getBytes()

This method encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.

19byte[] getBytes(Charset charset)

This method encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.

20byte[] getBytes(String charsetName)

This method encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.

21void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)

This method copies characters from this string into the destination character array.

22int hashCode()

This method returns a hash code for this string.

23int indexOf(int ch)

This method returns the index within this string of the first occurrence of the specified character.

24int indexOf(int ch, int fromIndex)

This method returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.

25int indexOf(String str)

This method returns the index within this string of the first occurrence of the specified substring.

26int indexOf(String str, int fromIndex)

This method returns the index within this string of the first occurrence of the specified substring, starting at the specified index.

27String intern()

This method returns a canonical representation for the string object.

28boolean isEmpty()

This method returns true if, and only if, length() is 0.

29int lastIndexOf(int ch)

This method returns the index within this string of the last occurrence of the specified character.

30int lastIndexOf(int ch, int fromIndex)

This method returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.

31int lastIndexOf(String str)

This method returns the index within this string of the rightmost occurrence of the specified substring.

32int lastIndexOf(String str, int fromIndex)

This method returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.

33int length()

This method returns the length of this string.

34boolean matches(String regex)

This method tells whether or not this string matches the given regular expression.

35int offsetByCodePoints(int index, int codePointOffset)

This method returns the index within this String that is offset from the given index by codePointOffset code points.

36boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)

This method tests if two string regions are equal with case ignored.

37boolean regionMatches(int toffset, String other, int ooffset, int len)

This method tests if two string regions are equal.

38String replace(char oldChar, char newChar)

This method returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.

39String replace(CharSequence target, CharSequence replacement)

This method replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.

40String replaceAll(String regex, String replacement)

This method replaces each substring of this string that matches the given regular expression with the given replacement.

41String replaceFirst(String regex, String replacement)

This method replaces the first substring of this string that matches the given regular expression with the given replacement.

42String[] split(String regex)

This method splits this string around matches of the given regular expression.

43String[] split(String regex, int limit)

This method splits this string around matches of the given regular expression.

44boolean startsWith(String prefix)

This method tests if this string starts with the specified prefix.

45boolean startsWith(String prefix, int toffset)

This method tests if the substring of this string beginning at the specified index starts with the specified prefix.

46CharSequence subSequence(int beginIndex, int endIndex)

This method returns a new character sequence that is a subsequence of this sequence.

47String substring(int beginIndex)

This method returns a new string that is a substring of this string.

48String substring(int beginIndex, int endIndex)

This method returns a new string that is a substring of this string.

49char[] toCharArray()

This method converts this string to a new character array.

50String toLowerCase()

This method converts all of the characters in this String to lower case using the rules of the default locale.

51String toLowerCase(Locale locale)

This method converts all of the characters in this String to lower case using the rules of the given Locale.

52String toString()

This method returns the string itself.

53String toUpperCase()

This method converts all of the characters in this String to upper case using the rules of the default locale.

54String toUpperCase(Locale locale)

This method converts all of the characters in this String to upper case using the rules of the given Locale.

55String trim()

This method returns a copy of the string, with leading and trailing whitespace omitted.

56static String valueOf(boolean b)

This method returns the string representation of the boolean argument.

57static String valueOf(char c)

This method returns the string representation of the char argument.

58static String valueOf(char[] data)

This method returns the string representation of the char array argument.

59static String valueOf(char[] data, int offset, int count)

This method Returns the string representation of a specific subarray of the char array argument.

60static String valueOf(double d)

This method returns the string representation of the double argument.

61static String valueOf(float f)

This method returns the string representation of the float argument.

62static String valueOf(int i)

This method returns the string representation of the int argument.

63static String valueOf(long l)

This method returns the string representation of the long argument.

64static String valueOf(Object obj)

This method returns the string representation of the Object argument.

Print Page
Previous
Next