StringBuffer in java

StringBuffer is a peer class of String that provides much of the functionality of strings. As you know, String represents fixed-length, immutable character sequences. In contrast, StringBuffer represents growable and writeable character sequences. StringBuffer may have characters and substrings inserted in the middle or appended to the end. StringBuffer will automatically grow to make room for such addition

StringBuffer Constructors

StringBuffer defines these four constructors:

StringBuffer( )
StringBuffer(int size)
StringBuffer(String str)
StringBuffer(CharSequence chars)

length( ) and capacity( )

The current length of a StringBuffer can be found via the length( ) method, while the total allocated capacity can be found through the capacity( ) method. They have the following general forms:

int length( )
int capacity( )

StringBuffer length vs. capacity

class StringBufferDemo {
public static void main(String args[]) {
StringBuffer sb = new StringBuffer("Hello");
System.out.println("buffer = " + sb);
System.out.println("length = " + sb.length());
System.out.println("capacity = " + sb.capacity());
}
}

buffer = Hello
length = 5
capacity = 21

append( )

The append( ) method concatenates the string representation of any other type of data to the end of the invoking StringBuffer object. It has several overloaded versions

Demonstrate append()

class appendDemo {
public static void main(String args[]) {
String s;
int a = 42;
StringBuffer sb = new StringBuffer(40);
s = sb.append("a = ").append(a).append("!").toString();
System.out.println(s);
}
}

Output

a = 42!

insert( )

The insert( ) method inserts one string into another. It is overloaded to accept values of all the simple types, plus Strings, Objects, and CharSequences. Like append( ), it calls String.valueOf( ) to obtain the string representation of the value it is called with. This string is then inserted into the invoking StringBuffer object. These are a few of its forms

StringBuffer insert(int index, String str)
StringBuffer insert(int index, char ch)
StringBuffer insert(int index, Object obj)

Demonstrate insert()

class insertDemo {
public static void main(String args[]) {
StringBuffer sb = new StringBuffer("I Java!");
sb.insert(2, "like ");
System.out.println(sb);
}
}

Output

I like Java!

reverse( )

Using reverse() to reverse a StringBuffer

class ReverseDemo {
public static void main(String args[]) {
StringBuffer s = new StringBuffer("abcdef");
System.out.println(s);
s.reverse();
System.out.println(s);
}
}

output produced by the program

abcdef
fedcba

delete( ) and deleteCharAt( )

Demonstrate delete() and deleteCharAt()

class deleteDemo {
public static void main(String args[]) {
StringBuffer sb = new StringBuffer("This is a test.");
sb.delete(4, 7);
System.out.println("After delete: " + sb);
sb.deleteCharAt(0);
System.out.println("After deleteCharAt: " + sb);
}
}

After delete: This a test.
After deleteCharAt: his a test.

replace( )

Demonstrate replace()

class replaceDemo {
public static void main(String args[]) {
StringBuffer sb = new StringBuffer("This is a test.");
sb.replace(5, 7, "was");
System.out.println("After replace: " + sb);
}
}

Output

After replace: This was a test

substring( )

String substring(int startIndex)
String substring(int startIndex, int endIndex)

Additional StringBuffer Methods