String, Char, StringBuilder, and StringBuffer

1. Overview

 Finding Different between String and Char. Check each role on JAVA.

 

3. Description

3.1 String

It's a Class having a class member of final char[] in it.

It has String Pool in JVM for caching literal reference of instance. but generated separate reference on the pool if instances are created using new keyword each time.

It's immutable like the final instance. So before JDK 1.5, if some concatenation occurred on already existing String instance, new allocation occurred. But from JDK 1.5 these operations using StringBuilder implicitly.

 

3.2 StringBuilder

Two Classes implements AbstractStringBuilder which doesn't have a final primitive char array, but sole primitive char array. So appending new String is possible in these classes' instances.

It's useful for concatenating Strings. Before JDK 1.5, Every Concatenating using + operator creates new String for storing which is inefficient. But from JDK 1.5, such operations using StringBuilder implicitly.

But StringBuilder is not thread-safe.

3.3 StringBuffer

It's thread-safe because using the synchronized keyword on appended, and so on.