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    Java String

    In Java, string is basically an object that represents sequence of char values. In java, objects of String are immutable which means a constant and cannot be changed once created.

    The java.lang.String class is used to create a string object.

    There are two ways to create String object:

    1. By string literal

    Java String literal is created by using double quotes.

    String s="welcome";  

    To make Java more memory efficient String literals are used (because no new objects are created if it exists already in the string constant pool).

    1. By new keyword

    String s=new String("welcome");

    In this case, JVM will create a new string object in normal (non-pool) heap memory, and the literal "Welcome" will be placed in the string constant pool. The variable s will refer to the object in a heap (non-pool).

    Example:

    public class StringEx{   

    public static void main(String args[]){   

    String s1="java";

    char ch[]={'s','t','r','i','n','g','s'};   

    String s2=new String(ch); //converting char array to string   

    String s3=new String("example"); //creating Java string by new keyword   

    System.out.println(s1);   

    System.out.println(s2);   

    System.out.println(s3);   

    }}   

    The java.lang.String class provides many useful methods to perform operations on sequence of char values.

    Method

    Description

    Return Type

    charAt()

    Returns the character at the specified index (position)

    char

    codePointAt()

    Returns the Unicode of the character at the specified index

    int

    codePointBefore()

    Returns the Unicode of the character before the specified index

    int

    codePointCount()

    Returns the Unicode in the specified text range of this String

    int

    compareTo()

    Compares two strings lexicographically

    int

    compareToIgnoreCase()

    Compares two strings lexicographically, ignoring case differences

    int

    concat()

    Appends a string to the end of another string

    String

    contains()

    Checks whether a string contains a sequence of characters

    boolean

    contentEquals()

    Checks whether a string contains the exact same sequence of characters of the specified CharSequence or StringBuffer

    boolean

    copyValueOf()

    Returns a String that represents the characters of the character array

    String

    endsWith()

    Checks whether a string ends with the specified character(s)

    boolean

    equals()

    Compares two strings. Returns true if the strings are equal, and false if not

    boolean

    equalsIgnoreCase()

    Compares two strings, ignoring case considerations

    boolean

    format()

    Returns a formatted string using the specified locale, format string, and arguments

    String

    getBytes()

    Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array

    byte[]

    getChars()

    Copies characters from a string to an array of chars

    void

    hashCode()

    Returns the hash code of a string

    int

    indexOf()

    Returns the position of the first found occurrence of specified characters in a string

    int

    intern()

    Returns the canonical representation for the string object

    String

    isEmpty()

    Checks whether a string is empty or not

    boolean

    lastIndexOf()

    Returns the position of the last found occurrence of specified characters in a string

    int

    length()

    Returns the length of a specified string

    int

    matches()

    Searches a string for a match against a regular expression, and returns the matches

    boolean

    offsetByCodePoints()

    Returns the index within this String that is offset from the given index by codePointOffset code points

    int

    regionMatches()

    Tests if two string regions are equal

    boolean

    replace()

    Searches a string for a specified value, and returns a new string where the specified values are replaced

    String

    replaceFirst()

    Replaces the first occurrence of a substring that matches the given regular expression with the given replacement

    String

    replaceAll()

    Replaces each substring of this string that matches the given regular expression with the given replacement

    String

    split()

    Splits a string into an array of substrings

    String[]

    startsWith()

    Checks whether a string starts with specified characters

    boolean

    subSequence()

    Returns a new character sequence that is a subsequence of this sequence

    CharSequence

    substring()

    Returns a new string which is the substring of a specified string

    String

    toCharArray()

    Converts this string to a new character array

    char[]

    toLowerCase()

    Converts a string to lower case letters

    String

    toString()

    Returns the value of a String object

    String

    toUpperCase()

    Converts a string to upper case letters

    String

    trim()

    Removes whitespace from both ends of a string

    String

    valueOf()

    Returns the string representation of the specified value

    String

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