Strings in Java

Strings in Java

A String represents a group of characters.A string is a predefined class meant for storing group of charactres.
The string objects can be created in 2 ways.

1.We can represents a string by enclosing a group of characters directly with in double codes" ".
             String s="hello";

2.We can create a string object by using "new" operator.

             String s=new String("hello");

-->The string objects created by both the mechanisms are called as "immutable objects".Immutable objects means the contents of that objects cann't be modified.

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.

After the following two lines of code have been executed, len equals 17:

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);

String  class Methods:

Here is the list of methods supported by String class:

1.char charAt(int index):Returns the character at the specified index.

 Ex: String str="java";
          System.out.println(str.ChatAt(1));

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.

The StringBuffer and StringBuilder classes are used when there is a necessity to make a lot of modifications to Strings of characters.

Unlike Strings objects of type StringBuffer and Stringbuilder can be modified over and over again with out leaving behind a lot of new unused objects.

The StringBuilder class was introduced as of Java 5 and the main difference between the StringBuffer and StringBuilder is that StringBuilders methods are not thread safe(not Synchronised).

It is recommended to use StringBuilder whenever possible because it is faster than StringBuffer. However if thread safety is necessary the best option is StringBuffer objects.
Example:

public class Test{

    public static void main(String args[]){
       StringBuffer sBuffer = new StringBuffer(" test");
       sBuffer.append(" String Buffer");
       System.ou.println(sBuffer); 
   }
}

This would produce the following result:

test String Buffer

StringBuffer Methods:

Here is the list of important methods supported by StringBuffer class:
SN    Methods with Description
1    public StringBuffer append(String s)
Updates the value of the object that invoked the method. The method takes boolean, char, int, long, Strings etc.
2    public StringBuffer reverse()
The method reverses the value of the StringBuffer object that invoked the method.
3    public delete(int start, int end)
Deletes the string starting from start index until end index.
4    public insert(int offset, int i)
This method inserts an string s at the position mentioned by offset.
5    replace(int start, int end, String str)
This method replaces the characters in a substring of this StringBuffer with characters in the specified String.

Here is the list of other methods (Except set methods ) which are very similar to String class:

1.int capacity():Returns the current capacity of the String buffer.
2.char charAt(int index):The specified character of the sequence currently represented by the string buffer, as indicated by the index argument, is returned.
3.void ensureCapacity(int minimumCapacity):Ensures that the capacity of the buffer is at least equal to the specified minimum.
4.void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin):Characters are copied from this string buffer into the destination character array dst.
5.int indexOf(String str):Returns the index within this string of the first occurrence of the specified substring.
6.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.
7.int lastIndexOf(String str):Returns the index within this string of the rightmost occurrence of the specified substring.
8.int lastIndexOf(String str, int fromIndex):Returns the index within this string of the last occurrence of the specified substring.
9.int length():Returns the length (character count) of this string buffer.
10.void setCharAt(int index, char ch):The character at the specified index of this string buffer is set to ch.
11.void setLength(int newLength):Sets the length of this String buffer.
12.CharSequence subSequence(int start, int end):Returns a new character sequence that is a subsequence of this sequence.
13.String substring(int start):Returns a new String that contains a subsequence of characters currently contained in this StringBuffer.The substring begins at the specified index and extends to the end of the StringBuffer.
14.String substring(int start, int end):Returns a new String that contains a subsequence of characters currently contained in this StringBuffer.
15.String toString():Converts to a string representing the data in this string buffer.

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