StringBuffer class in Java
StringBuffer class is used to create a mutable string object. It means, it can be changed after it is created. It represents growable and writable character sequence.
It is similar to String class in Java both are used to create string, but stringbuffer object can be changed.
So StringBuffer class is used when we have to make lot of modifications to our string. It is also thread safe i.e multiple threads cannot access it simultaneously. StringBuffer defines 4 constructors.
- StringBuffer(): It creates an empty string buffer and reserves space for 16 characters.
- StringBuffer(int size): It creates an empty string and takes an integer argument to set capacity of the buffer.
- StringBuffer(String str): It creates a stringbuffer object from the specified string.
- StringBuffer(charSequence []ch): It creates a stringbuffer object from the charsequence array.
Example: Creating a StringBuffer Object
In this example, we are creating string buffer object using StrigBuffer class and also testing its mutability.
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Example: difference between String and StringBuffer
In this example, we are creating objects of String and StringBuffer class and modifying them, but only stringbuffer object get modified. See the below example.
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Explanation:
Output is such because String objects are immutable objects. Hence, if we concatenate on the same String object, it won’t be altered But StringBuffer creates mutable objects. Hence, it can be altered.
Important methods of StringBuffer class
The following methods are some most commonly used methods of StringBuffer class.
append()
This method will concatenate the string representation of any type of data to the end of the StringBuffer object. append()
method has several overloaded forms.
The string representation of each parameter is appended to StringBuffer object.
test123
insert()
This method inserts one string into another. Here are few forms of insert()
method.
Here the first parameter gives the index at which position the string will be inserted and string representation of second parameter is inserted into StringBuffer object.
test123
reverse()
This method reverses the characters within a StringBuffer object.
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replace()
This method replaces the string from specified start index to the end index.
Hello java
capacity()
This method returns the current capacity of StringBuffer object.
16
Note: Empty constructor reserves space for 16 characters. Therefore the output is 16.
ensureCapacity()
This method is used to ensure minimum capacity of StringBuffer object.
If the argument of the ensureCapacity() method is less than the existing capacity, then there will be no change in existing capacity.
If the argument of the ensureCapacity() method is greater than the existing capacity, then there will be change in the current capacity using following rule: newCapacity = (oldCapacity*2) + 2.
16 34