JAVA - STRINGS CLASS
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Strings, which are widely used in Java programming, are a sequence of characters. In the Java
programming language, strings are 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 eleven constructors that allow you to provide the initial value of
the string using different sources, such as an array of characters.
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 would produce the following result:
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.
Below given program is an example of length , method String class.
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 would produce the following result:
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:
public class StringDemo {
public static void main(String args[]) {
String string1 = "saw I was ";
System.out.println("Dot " + string1 + "Tod");
}
}
This would produce the following result:
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:
SN Methods with Description
1
char charAtintindex
Returns the character at the specified index.
2
int compareToObjecto
Compares this String to another Object.
3
int compareToStringanotherString
Compares two strings lexicographically.
4
int compareToIgnoreCaseStringstr
Compares two strings lexicographically, ignoring case differences.
5
String concatStringstr
Concatenates the specified string to the end of this string.
6
boolean contentEqualsStringBuffersb
Returns true if and only if this String represents the same sequence of characters as the
specified StringBuffer.
7
static String copyValueOfchar[]data
Returns a String that represents the character sequence in the array specified.
8
static String copyValueOfchar[]data, intoffset, intcount
Returns a String that represents the character sequence in the array specified.
9
boolean endsWithStringsuffix
Tests if this string ends with the specified suffix.
10
boolean equalsObjectanObject
Compares this string to the specified object.
11
boolean equalsIgnoreCaseStringanotherString
Compares this String to another String, ignoring case considerations.
12
byte getBytes
Encodes this String into a sequence of bytes using the platform's default charset, storing
the result into a new byte array.
13
13
byte[] getBytes(String charsetName
Encodes this String into a sequence of bytes using the named charset, storing the result
into a new byte array.
14
void getCharsintsrcBegin, intsrcEnd, char[]dst, intdstBegin
Copies characters from this string into the destination character array.
15
int hashCode
Returns a hash code for this string.
16
int indexOfintch
Returns the index within this string of the first occurrence of the specified character.
17
int indexOfintch, intfromIndex
Returns the index within this string of the first occurrence of the specified character,
starting the search at the specified index.
18
int indexOfStringstr
Returns the index within this string of the first occurrence of the specified substring.
19
int indexOfStringstr, intfromIndex
Returns the index within this string of the first occurrence of the specified substring,
starting at the specified index
20
String intern
Returns a canonical representation for the string object.
21
int lastIndexOfintch
Returns the index within this string of the last occurrence of the specified character.
22
int lastIndexOfintch, intfromIndex
Returns the index within this string of the last occurrence of the specified character,
searching backward starting at the specified index.
23
int lastIndexOfStringstr
Returns the index within this string of the rightmost occurrence of the specified substring.
24
24
int lastIndexOfStringstr, intfromIndex
Returns the index within this string of the last occurrence of the specified substring,
searching backward starting at the specified index.
25
int length
Returns the length of this string.
26
boolean matchesStringregex
Tells whether or not this string matches the given regular expression.
27
boolean regionMatchesbooleanignoreCase, inttoffset, Stringother, intooffset, intlen
Tests if two string regions are equal.
28
boolean regionMatchesinttoffset, Stringother, intooffset, intlen
Tests if two string regions are equal
29
String replacecharoldChar, charnewChar
Returns a new string resulting from replacing all occurrences of oldChar in this string with
newChar.
30
String replaceAll(String regex, String replacement
Replaces each substring of this string that matches the given regular expression with the
given replacement.
31
String replaceFirstStringregex, Stringreplacement
Replaces the first substring of this string that matches the given regular expression with
the given replacement.
32
String[] splitStringregex
Splits this string around matches of the given regular expression.
33
String[] splitStringregex, intlimit
Splits this string around matches of the given regular expression.
34
boolean startsWithStringprefix
Tests if this string starts with the specified prefix.
35
35
boolean startsWithStringprefix, inttoffset
Tests if this string starts with the specified prefix beginning a specified index.
36
CharSequence subSequenceintbeginIndex, intendIndex
Returns a new character sequence that is a subsequence of this sequence.
37
String substringintbeginIndex
Returns a new string that is a substring of this string.
38
String substringintbeginIndex, intendIndex
Returns a new string that is a substring of this string.
39
char[] toCharArray
Converts this string to a new character array.
40
String toLowerCase
Converts all of the characters in this String to lower case using the rules of the default
locale.
41
String toLowerCaseLocalelocale
Converts all of the characters in this String to lower case using the rules of the given
Locale.
42
String toString
This object whichisalreadyastring! is itself returned.
43
String toUpperCase
Converts all of the characters in this String to upper case using the rules of the default
locale.
44
String toUpperCaseLocalelocale
Converts all of the characters in this String to upper case using the rules of the given
Locale.
45
String trim
Returns a copy of the string, with leading and trailing whitespace omitted.
46
46
static String valueOfprimitivedatatypex
Returns the string representation of the passed data type argument.
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