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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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