Difference between StringBuffer and StringBuilder

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StringBuffer and StringBuilder are two important classes in Java which represents mutable String i.e. the String object, whose value can be changed. Since String is Immutable in Java, any change or operation on String object e.g. converting it to upper or lower case, adding character, removing character or substring all result in a new String object. This can put a lot of pressure on Garbage collector if your application generates lots of throws away String instances, to avoid this issue, Java designer presented initially StringBuffer class and later StringBuilder. When StringBuffer was introduced it has its own problem e.g. it was synchronized and hence was a lot slower.

Since it is mostly used as local variable making it synchronized wasn't a great decision and Java designer realizes their mistake and corrected it in Java 1.5 by introducing StringBuilder class. StringBuilder was nothing but a drop in like to like a class for StringBuffer except that its method was not synchronized. In this article, I'll tell you some of the important points you should know about StringBuilder and StringBuffer class.

10 Differences between StringBuffer and StringBuilder in Java

  1. StringBuffer is present in Java and StringBuilder was added in Java 5.

  2. Both StringBuffer and StringBuilder represents mutable String which means you can add/remove characters, substring without creating new objects.

  3. You can convert a StringBuffer into String by calling toString() method.

  4. Both StringBuilder and StringBuffer doesn't override equals() and hashCode() method because they are mutable and not intended to be used as a key in hash based collection classes e.g. HashMap, Hashtable, and HashSet.

  5. StringBuffer is synchronized which means all method which modifies the internal data of StringBuffer is synchronized e.g. append(), insert() and delete(). On contrary, StringBuilder is not synchronized.

  6. Because of synchronization StringBuffer is considered thread safe e.g. multiple threads can call its method without compromising internal data structure but StringBuilder is not synchronized hence not thread safe. See Java, A Beginners Guide for more details.

  7. Differences between StringBuffer and StringBuilder in Java

  8. Another side effect of synchronization is speed. Since StringBuffer is synchronized its lot slower than StringBuilder.

  9. The default length of StringBuffer is 16 characters. You should explicitly define the size of it, especially if you know that size would be less or more than 16 to avoid wasting memory and spending time during resize.

There are many differences between StringBuffer and StringBuilder. A list of differences between StringBuffer and StringBuilder are given below

No.StringBufferStringBuilder
1)StringBuffer is synchronized i.e. thread safe. It means two threads can't call the methods of StringBuffer simultaneously.StringBuilder is non-synchronized i.e. not thread safe. It means two threads can call the methods of StringBuilder simultaneously.
2)StringBuffer is less efficient than StringBuilder.StringBuilder is more efficient than StringBuffer.
StringBuffer Example

import java.io.*;
public class Test
{  
public static void main(String[] args)
   {  
        StringBuffer buffer=new StringBuffer("hello");  
        buffer.append("java");  
        System.out.println(buffer);  
    }  
}


Output:


hellojava
StringBuilder Example

import java.io.*;
public class Test
{  
public static void main(String[] args)
   {  
        StringBuilder builder=new StringBuilder("hello");  
        builder.append("java program");  
        System.out.println(builder);  
    }  
}


Output:


hellojava program
Performance Test of StringBuffer and StringBuilder

See the code to check the performance of StringBuffer and StringBuilder classes.


import java.io.*;
public class Test
{  
public static void main(String[] args)
   {  
        long startTime = System.currentTimeMillis();  
        StringBuffer sb = new StringBuffer("cprogrmming");  
        for (int i=0; i<11000; i++){  
            sb.append("coding");  
        }  
        System.out.println("Time taken by StringBuffer: " + (System.currentTimeMillis() - startTime) + "ms");  
        startTime = System.currentTimeMillis();  
        StringBuilder sb2 = new StringBuilder("cprogrmming");  
        for (int i=0; i<11000; i++){  
            sb2.append("coding");  
        }  
        System.out.println("Time taken by StringBuilder: " + (System.currentTimeMillis() - startTime) + "ms");  
    }  
}


Output:

Time taken by StringBuffer: 5ms
Time taken by StringBuilder: 8ms



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