Java - Differences between String, StringBuffer and StringBuilder

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First of all we know String is one of the most important class in java and [String is immutable and final class in java][]. This means every modification in String creates a new string object like trim(), toUpperCase(), toLowerCase() etc.

String object cached in String Pool memory in java. So in large application we should always care about creating the String object using new keyword, it always create new object instead of using cached object of same string value. While working on large application, you work with heavy usage of String, but if you do profiling of your application, then you will find that String is the one of the class which creates lots of garbage because of many temporary String objects created in program.

In java there are two more classes available for string manipulation. These classes are StringBuilder and StringBuffer. In java StringBuilder was added in JDK 5 but StringBuffer is old class. These two classes solve issues related string class.

# String class in Java #

Lets see some properties about these classes first before differences between them.

1. String is immutable in Java. In java, [string class is immutable because String objects][] are cached in String pool. Immutable means unmodifiable or unchangeable, means once string object is created its data or state can’t be changed but a new string object is created. Immutability nature of String class provides lot of benefit, in HashMap its hashcode value is cached which makes it a faster hashmap key. String class’s final nature provide benefit to safely shared into multiple threads without need of any synchronization.

2. In java, we can create String objects in two ways. One is created with new keyword and other created by using literal. If we create string object by using literal, then this value is cached to string pool. Whenever required another string with same value, it assigns same cached object of string instead of creating new object.

For example:

String str1= "Java";
    String str2= "Java";

![String immutable][]

3. Here we represent string in double quotes “java”, they are referred as String literal and created in String pool. So, when you compare two String literals using equality operator “==” it returns true because they are actually the same instance of String.

4. When we use “+” operator for two or more strings concatenation then it creates new string after concatenation of all given values of string, internally “+” operation is implemented using either StringBuffer or StringBuilder.

5. String class in java [overrides equals() and hashcode()][overrides equals_ and hashcode] method of object class because of two Strings should be consider equal if they contain exactly same characters. In [java collection][] there are many sorted collections like SortedSet, SortedMap etc. and for these collections string is used as key so it must be consistent with compareTo() method for String.

6. String is represented using UTF-16 format in Java.

7. String object can be created by multiple ways such as char array, byte array, from another string, from StringBuffer and from StringBuidler. String class provides many more overloaded constructors of supporting mutliple ways to create string object.

# Problem with String #

The main problem with String is consuming large space if it is not used properly. This problem of string is due to immutability nature of String. Any modification in string like trim(), toUpperCase(), toLowerCase(), getting sub-string and concatenation with other string etc. Since String is an immutable class, every time a new String is created and older one is discarded which creates lots of temporary garbage in heap. Let see with example as below.

// To declare a new String object
    String str1 = "Hello";
    
    // To declare another String object
    String str2 = " Java";
    
    // When we concatenate two string objects then it will create a new object in memory
    str2 = str1 + str2;

![Differences between String, StringBuffer and StringBuilder in Java][Differences between String_ StringBuffer and StringBuilder in Java]

# String vs StringBuffer #

String is immutable while StringBuffer is mutable. It means you can not modify a String object but you can modify StringBuffer object after creating it without creating any new object. This mutable nature of StringBuffer class solves the problems generated by immutable nature of String.

We can convert StringBuffer to String class by using toString() method.

Below is the example of String and StringBuffer:

// To declare a new String object
    String str1 = "Hello";
    String str2 = " Java";
    // When we concatenate any new value to string then it creates a new object in memory
    str2 = str1 + str2;

Solve the space problem with using StringBuffer:

// To declare a StringBuffer object
    StringBuffer sb = new StringBuffer("Hello");
    sb.append(" Java");

# StringBuilder vs StringBuffer #

StringBuilder is one more class added to JDK as of version 5 of Java. This class also provides functionality of String and StringBuffer but there are following points that makes StringBuilder different from StringBuffer and String.

All methods of StringBuffer class are synchronized because of making it thread-safe, but same time slow. But StringBuilder is not synchronized. In java 5 StringBuilder is a copy of StringBuffer but without synchronization. Try to use StringBuilder whenever possible it performs better in most of the cases than StringBuffer class.

If you want to concatenate two strings by using “+” then “+” operation is internally implemented using either StringBuffer or StringBuilder in Java.

Below is the example of StringBuilder and StringBuffer:

// To declare a new StringBuffer object
    StringBuffer buffer = new StringBuffer("Hello");
    buffer.append(" Java");
    
    // To declare a new StringBuilder object
    StringBuilder builder = new StringBuilder("Hello");
    builder.append(" Java");

If you see above example of StringBuilder and StringBuffer, you will find that they are exactly similar and all API methods applicable to StringBuffer are also applicable to StringBuilder.

# Summary #

Java provides three classes String, StringBuffer and StringBuilder with different purposes. But these classes are all used to manipulate string. The following points we found to make these differ in functionalities for same target.

*  String is immutable in nature while StringBuffer and StringBuilder is mutable
 *  StringBuffer is synchronized while StringBuilder is not
 *  StringBuilder is faster than StringBuffer becuase of StringBuffer is thread-safe
 *  Concatenation operator “+” for String is internally implemented using either StringBuffer or StringBuilder
 *  Use String if immutability is required
 *  Use StringBuffer if you need mutable with thread-safety
 *  Use StringBuilder if you require mutable without thread-safety

[http_www.captainbed.net]: http://www.captainbed.net/troubleshooter
[String is immutable and final class in java]: https://www.dineshonjava.com/how-to-make-java-class-immutable/
[string class is immutable because String objects]: https://www.dineshonjava.com/2014/11/how-to-make-java-class-immutable.html
[String immutable]: /images/20220529/bd32b9db28e9492c852e008c437d53a8.png
[overrides equals_ and hashcode]: https://www.dineshonjava.com/2017/02/hashcode-and-equals-methods-in-java.html
[java collection]: https://www.dineshonjava.com/2013/01/core-java-baby-step-to-be-best-java-ian.html#Collection_Classes
[Differences between String_ StringBuffer and StringBuilder in Java]: /images/20220529/001fad9c4af1465a9bd59ee6dc7a57fb.png