String
String is immutable ( once created can not be changed )object . The object created as a String is stored in the Constant String Pool . They are thread safe.
StringBuffer
StringBuffer is mutable means one can change the value of the object . Object created through StringBuffer is stored in the heap. Each method in StringBuffer is synchronized that is StringBuffer is thread safe
StringBuilder
StringBuilder is same as the StringBuffer , that is it stores the object in heap and it can also be modified . StringBuilder is also not thread safe.
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