What is the difference between stringbuffer and stringbuilder class in java?

String objects are immutable whereas StringBuffer and StringBuilder objects are mutable.
StringBuffer and StringBuilder are same only difference is that StringBuilder is not synchronized whereas StringBuffer is. As StringBuilder is not synchronized, it is not thread safe but faster than StringBuffer.
Use String, for a string which will be constant through out the application.
Use StringBuffer, for a string which can change in multi-threaded applications.
Use StringBuilder, for a string which can change in single-threaded applications.

Example of String, StringBuffer and StringBuilder

public class Main 
{ 
    long startTime = 0l;
    long endTime = 0l;
    long timeDiff = 0l;
    // Concatenate operation using String 
    public void concatTest1(String website) 
    { 
        startTime = System.nanoTime();
        website = website + ".com";
        endTime = System.nanoTime();
        timeDiff = endTime - startTime;
        System.out.println("Concat time by String: " + timeDiff);
    } 
 
    // Concatenate operation using StringBuilder 
    public void concatTest2(StringBuilder website) 
    {  
        startTime = System.nanoTime();
        website.append(".com"); 
        endTime = System.nanoTime();
        timeDiff = endTime - startTime;
        System.out.println("Concat time by StringBuilder: " + timeDiff);
    } 
 
    // Concatenate operation using StringBuffer 
    public void concatTest3(StringBuffer website) 
    { 
        startTime = System.nanoTime();
        website.append(".com");
        endTime = System.nanoTime();
        timeDiff = endTime - startTime;
        System.out.println("Concat time by StringBuffer: " + timeDiff);
    } 
 
    public static void main(String[] args) 
    { 
        Main object = new Main();
        String website1 = "w3spoint"; 
        object.concatTest1(website1);
 
        StringBuilder website2 = new StringBuilder("w3spoint"); 
        object.concatTest2(website2);
 
        StringBuffer website3 = new StringBuffer("w3spoint"); 
        object.concatTest3(website3); 
    } 
}

Output

Concat time by String: 43970
Concat time by StringBuilder: 760
Concat time by StringBuffer: 3470

Conversion between types of strings in Java

String to StringBuffer and StringBuilder

Example

public class Main 
{ 
 
    public static void main(String[] args) 
    { 
        String stringObj = "w3spoint"; 
 
        System.out.println("String Object: " + stringObj);  
 
        // String to StringBuffer 
        StringBuffer stringBuffer = new StringBuffer(stringObj); 
        System.out.println("StringBuffer Object: " + stringBuffer);
        stringBuffer.reverse();
        System.out.println("StringBuffer Object after reverse operation: " + stringBuffer);
 
        //String to StringBuilder 
        StringBuilder stringBuilder = new StringBuilder(stringObj); 
        System.out.println("StringBuilder Object: " + stringBuilder);
        stringBuilder.append(".com"); 
        System.out.println("StringBuilder Object after append operation: " + stringBuilder);
    } 
 
}

Output

String Object: w3spoint
StringBuffer Object: w3spoint
StringBuffer Object after reverse operation: tniops3w 
StringBuilder Object: w3spoint
StringBuilder Object after append operation: w3spoint.com

StringBuffer and StringBuilder to String

Example

public class Main 
{ 
    void stringBufferToString(StringBuffer stringBuffer){
        String stringObj = stringBuffer.toString(); 
        System.out.println("Converted String from StringBuffer: " + stringObj); 
    }
 
    void stringBuilderToString(StringBuilder stringBuilder){
        String stringObj = stringBuilder.toString(); 
        System.out.println("Converted String from StringBuilder: " + stringObj); 
    }
 
    public static void main(String[] args) 
    {   
        StringBuffer stringBuffer = new StringBuffer("w3spoint"); 
        StringBuilder stringBuilder = new StringBuilder("w3spoint");
        Main main = new Main();
        main.stringBufferToString(stringBuffer);
        main.stringBuilderToString(stringBuilder);
    } 
 
}

Output

Converted String from StringBuffer: w3spoint
Converted String from StringBuilder: w3spoint

StringBuffer to StringBuilder or StringBuilder to StringBuffer

Example

public class Main 
{ 
    void stringBufferToStringBuilder(StringBuffer stringBuffer){
        String stringObj = stringBuffer.toString(); 
        StringBuilder stringBuilder = new StringBuilder(stringObj);
        System.out.println("Converted StringBuilder from StringBuffer: " + stringObj); 
    }
 
    void stringBuilderToStringBuffer(StringBuilder stringBuilder){
        String stringObj = stringBuilder.toString(); 
        StringBuffer stringBuffer = new StringBuffer(stringObj); 
        System.out.println("Converted StringBuffer from StringBuilder: " + stringObj); 
    }
 
    public static void main(String[] args) 
    {   
        StringBuffer stringBuffer = new StringBuffer("w3spoint"); 
        StringBuilder stringBuilder = new StringBuilder("w3spoint");
        Main main = new Main();
        main.stringBufferToStringBuilder(stringBuffer);
        main.stringBuilderToStringBuffer(stringBuilder);
    } 
 
}

Output

Converted StringBuilder from StringBuffer: w3spoint 
Converted StringBuffer from StringBuilder: w3spoint

Java interview questions on String Handling

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