StringBuilder in java

StringBuilder in java is like a String ,but which can be modified. It is same as StringBuffer, but only difference is that it is non-synchronized. The length of the String and content of sequence can be changed by using StringBuilder methods.

It can be implemented in following ways.

1. StringBuilder (): creates an empty string Builder with the initial capacity of 16.
2. StringBuilder (String str): creates a string builder with the specified string.
3. StringBuilder (int capacity): Capacity is the no. of character it can hold.It increases automatically as more contents added to it.

 

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It provides mutable String.

If String can be modified ,called a mutable String. It can be achieved by StringBuilder class.

Useful methods of StringBuilder :

1. append() method:

This method appends a new String into the existing String.

public class ExampleStringBuilder {
	public static void main(String[] args) {
		
		StringBuilder str = new StringBuilder("House");
		System.out.println(str.append(" is beautiful"));	
	}
}

2. Length() method:

This method will give you the length of the String.

public class ExampleStringBuilder {
	public static void main(String[] args) {
		
		StringBuilder str = new StringBuilder("House");
		System.out.println(str.length());	 
	}
}

3. replace() method:

This method will replace substring taken its start position and end position , with  a new substring.

public class ExampleStringBuilder  {
	public static void main(String[] args) {
		
		StringBuilder str = new StringBuilder("This is a House");
		System.out.println(str.replace(5, 7, "was"));	  // results : This was a House 
	}
}

4. insert() method:

This method is used to insert a new String to an existing string.

public class ExampleStringBuilder  {
	public static void main(String[] args) {
		
		StringBuilder str = new StringBuilder("This is a House");
		System.out.println(str.insert(0, "Yes, "));	  
	}
}

5. subString() method:

It will return a substring extracted

public class ExampleStringBuilder {
	public static void main(String[] args) {
		
		StringBuilder str = new StringBuilder("This is a House");
		System.out.println(str.substring(8));	  
	}
}

from a start point.

6. Delete() method:

This will delete a part of the String mentioned in the start and end point.

public class ExampleStringBuilder {
	public static void main(String[] args) {
		
		StringBuilder str = new StringBuilder("This is a House");
		System.out.println(str.delete(0, 8));	  
	}
}

7. reverse() method:

This method returns a reversed String.

public class ExampleStringBuilder  {
	public static void main(String[] args) {
		
		StringBuilder str = new StringBuilder("This is a House");
		System.out.println(str.reverse());	  
	}
}

8. Capacity() method:

This method  returns the current capacity of the buffer. The default capacity of the buffer is 16. If the number of character increases from its current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.

public class ExampleStringBuilder  {
	public static void main(String[] args) {
		StringBuilder str1 = new StringBuilder();
		System.out.println(str1.capacity());    // returns 16
		
		str1.append("House");
		System.out.println(str1.capacity());    // returns 16
		
		StringBuilder str2 = new StringBuilder("This is a House");
		System.out.println(str2.capacity());	   // returns 31
	}
}