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Java Strings

Strings are one of the most common data types in Java. It is used for storing text. It can be created by enclosing characters in double quotation marks. It can be assigned to a variable using = sign.

String MyString = "Hello World!";

String Length

A String in Java is an object and the String object has a method called length() which can be used to find the total number of characters in the String.

public class MyClass {
  public static void main(String[] args) {
    String MyString = "Hello World!";
    System.out.println(MyString.length());  
  }
}

The output of the above code will be:

12

Check a character in the String

Java String has indexOf() method which returns index position of first occurrence of specified text in the string. Please note that, Java counts index position from 0.

public class MyClass {
  public static void main(String[] args) {
    String MyString = "Hello World!";
    System.out.println(MyString.indexOf("Wor"));  
  }
}

The above code will give the following output:

6

String Concatenation

In Java, two strings can be joined using + operator. Along with this, Java String has concat() method which can also be used to combine two strings.

public class MyClass {
  public static void main(String[] args) {
    String text_1 = "Learn ";
    String text_2 = "Java ";
    String text_3 = "with AlphaCodingSkills.com";
    System.out.println(text_1 + text_2 + text_3); 
    System.out.println(text_1.concat(text_2).concat(text_3));  
  }
}

The above code will give the following output:

Learn Java with AlphaCodingSkills.com
Learn Java with AlphaCodingSkills.com

Special Strings in String

The backslash \ escape character is used to convert special character like single quote, double quote, new line, etc. into the string character. The below mentioned table describes special characters in Java:

Escape CharacterResultExample
\' ' "\'Java\'" is converted into: 'Java'
\" " "\"World\"" is converted into: "World"
\\ \ "A\\C" is converted into: A\C
\n new line "Hello\nJohn" is converted into:
Hello
John
\t Tab "Hello\tMarry" is converted into: Hello    Marry
\b Backspace "Hello J\bava" is converted into: Hello ava
\r Carriage Return "Hello\rJohn" is converted into:
Hello
John

Note:Carriage return is not same as new line. It simply means return to the left margin.

String Methods

For complete list of string methods, please refer to string methods page. Here, few very common string methods are discussed.

  • toLowerCase(): Returns string in lowercase
  • toUpperCase(): Returns string in uppercase
  • trim(): Removes whitespaces from start and end of the string
  • replace(): replace specified character(s) with another specified character(s)

Example: toLowerCase() and toUpperCase() String Methods


public class MyClass {
  public static void main(String[] args) {
    String MyString = "Learn Java";
    System.out.println(MyString.toLowerCase()); 
    System.out.println(MyString.toUpperCase());  
  }
}

The above code will give the following output:

learn java
LEARN JAVA

Example: trim() and replace() String Methods


public class MyClass {
  public static void main(String[] args) {
    String MyString = "  Hello World!  ";
    System.out.println(MyString.trim()); 
    System.out.println(MyString.replace("World!", "Java"));  
  }
}

The above code will give the following output:

Hello World!
  Hello Java 

Java String Methods
MethodDescription
charAt() Returns the character at the specified index.
codePointAt() Returns the Unicode of the character at the specified index.
codePointBefore() Returns the Unicode of the character before the specified index.
codePointCount() Returns the number of Unicode code points in the specified text range.
compareTo() Compares two strings lexicographically.
compareToIgnoreCase() Compares two strings lexicographically, ignoring case differences.
concat() Appends a string to the end of another string.
contains() Returns true if the string contains the specified sequence of char values.
contentEquals() Compares the string to the specified CharSequence.
copyValueOf() Returns a String that represents the characters of the character array.
endsWith() Checks whether a string ends with the specified character(s).
equals() Compares two strings. Returns true if the strings are equal, and false if not.
equalsIgnoreCase() Compares two strings, ignoring case considerations.
format() Returns a formatted string using the specified locale, format string, and arguments.
getBytes() Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
getChars() Copies characters from a string to an array of chars.
hashCode() Returns the hash code of a string.
indexOf() Returns the position of the first found occurrence of specified characters in a string.
intern() Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
isEmpty() Checks whether a string is empty or not.
join() Returns a new string composed of CharSequence elements joined together with the specified delimiter.
lastIndexOf() Returns the position of the last found occurrence of specified characters in a string.
length() Returns the length of a specified string.
matches() Searches a string for a match against a regular expression, and returns the matches.
offsetByCodePoints() Returns the index within this String that is offset from the given index by codePointOffset code points.
regionMatches() Tests if two string regions are equal.
replace() Searches a string for a specified value, and returns a new string where the specified values are replaced.
replaceFirst() Replaces the first occurrence of a substring that matches the given regular expression with the given replacement.
replaceAll() Replaces each substring of this string that matches the given regular expression with the given replacement.
split() Splits a string into an array of substrings.
startsWith() Checks whether a string or substring of a string starts with specified prefix.
subSequence() Returns a new character sequence that is a subsequence of this sequence.
substring() Extracts the characters from a string, beginning at a specified start position, and through the specified number of character.
toCharArray() Converts this string to a new character array.
toLowerCase() Converts a string to lower case letters.
toString() Returns the value of a String object.
toUpperCase() Converts a string to upper case letters.
trim() Removes whitespace from both ends of a string.
valueOf() Returns the string representation of the given argument.