STRING IN JAVA


What Is String?

A string is a sequence of characters. In the Java programming language, strings are objects.strings are not primitive data types in Java, and therefore need to be represented by a class. Java has a class named String to represent string objects.

String represents fixed-length, immutable character sequences

Declaration Of String

String e = " "; // an empty string

String name = new String("Ravi");

The String class has thirteen constructors that allow you to provide the initial value of the string using different sources, such as an array of characters

char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };

String helloString = new String(helloArray);

System.out.println(helloString);

String Length

length() method returns the number of characters contained in the string object.

String name = "Mohan";

int len = name.length();

Concatenating Strings

The String class includes a method for concatenating two strings

String string1="Ravi";

String string2=" Kumar";

string1.concat(string2);

This returns a new string that is string1 with string2 added to it at the end.

i.e. Ravi Kumar

Strings are more commonly concatenated with the + operator

"Hello," + " world" + "!"

which results in

"Hello, world!"

The + operator is widely used in print statements. For example

String string1 = "is a ";

System.out.println("Ravi " + string1 + "good painter.");

which prints

Ravi is a good painter.

Such a concatenation can be a mixture of any objects. For each object that is not a String, its toString() method is called to convert it to a String.


Creating Format Strings

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 s;

s = 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(s);

Conversion Between Numbers and Strings

To convert a number to a string you need to operate on the value in its string form. There are several easy ways to convert a number to a string.

int i;

// Concatenate "i" with an empty string; conversion is handled for you.

String s1 = "" + i;

or

// The valueOf class method.

String s2 = String.valueOf(i);

Each of the Number subclasses includes a class method, toString(), that will convert its primitive type to a string. For example:

int i;

double d;

String s3 = Integer.toString(i);

String s4 = Double.toString(d);

String Methods

Here is the list of methods supported by String class −

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

Returns the character at the specified index.
2 int compareTo(Object o)

Compares this String to another Object.
3 int compareTo(String anotherString)

Compares two strings lexicographically.
4 int compareToIgnoreCase(String str)

Compares two strings lexicographically, ignoring case differences.
5 String concat(String str)

Concatenates the specified string to the end of this string.
6 boolean contentEquals(StringBuffer sb)

Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
7 static String copyValueOf(char[] data)

Returns a String that represents the character sequence in the array specified.
8 static String copyValueOf(char[] data, int offset, int count)

Returns a String that represents the character sequence in the array specified.
9 boolean endsWith(String suffix)

Tests if this string ends with the specified suffix.
10 boolean equals(Object anObject)

Compares this string to the specified object.
11 boolean equalsIgnoreCase(String anotherString)

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

Copies characters from this string into the destination character array.
15 int hashCode()

Returns a hash code for this string.
16 int indexOf(int ch)

Returns the index within this string of the first occurrence of the specified character.
17 int indexOf(int ch, int fromIndex)

Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
18 int indexOf(String str)

Returns the index within this string of the first occurrence of the specified substring.
19 int indexOf(String str, int fromIndex)

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 lastIndexOf(int ch)

Returns the index within this string of the last occurrence of the specified character.
22 int lastIndexOf(int ch, int fromIndex)

Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
23 int lastIndexOf(String str)

Returns the index within this string of the rightmost occurrence of the specified substring.
24 int lastIndexOf(String str, int fromIndex)

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 matches(String regex)

Tells whether or not this string matches the given regular expression.
27 boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)

Tests if two string regions are equal.
28 boolean regionMatches(int toffset, String other, int ooffset, int len)

Tests if two string regions are equal.
29 String replace(char oldChar, char newChar)

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 replaceFirst(String regex, String replacement)

Replaces the first substring of this string that matches the given regular expression with the given replacement.
32 String[] split(String regex)

Splits this string around matches of the given regular expression.
33 String[] split(String regex, int limit)

Splits this string around matches of the given regular expression.
34 boolean startsWith(String prefix)

Tests if this string starts with the specified prefix.
35 boolean startsWith(String prefix, int toffset)

Tests if this string starts with the specified prefix beginning a specified index.
36 CharSequence subSequence(int beginIndex, int endIndex)

Returns a new character sequence that is a subsequence of this sequence.
37 String substring(int beginIndex)

Returns a new string that is a substring of this string.
38 String substring(int beginIndex, int endIndex)

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 toLowerCase(Locale locale)

Converts all of the characters in this String to lower case using the rules of the given Locale.
42 String toString()

This object (which is already a string!) 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 toUpperCase(Locale locale)

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 static String valueOf(primitive data type x)

Returns the string representation of the passed data type argument.