What is the immutable object? What is the difference between creating String as new () and literal? What is difference between Strings vs. StringBuffer vs. StringBuilder in Java?

What is the immutable object? What is the difference between creating String as new () and literal? What is difference between Strings vs. StringBuffer vs. StringBuilder in Java?

Immutable object:

Immutable classes are Java classes whose objects cannot be modified once created. Any modification in Immutable object results in a new object. For example, is String is immutable in Java. Mostly Immutable are also final in Java, in order to prevent sub class from overriding methods in Java which can compromise Immutability. You can achieve the same functionality by making member as non-final but private and not modifying them except in constructor.

Difference between creating String as new() and literal:

·         String with new() Operator, it’s created in heap and not added into string pool.

·         String created using literal are created in String pool itself which exists in PermGen area of heap.

            String s = new String("Test");

·         Does not put the object in String pool, we need to call String.intern() method which is used to put them into the String pool explicitly.

·         It’s only when you create String object as String literal e.g. String s = "Test" Java automatically put that into String pool.

Difference between Strings vs. StringBuffer vs. StringBuilder in Java:

·         String is immutable whereas StringBuffer and StringBuilder are mutable classes.

·         StringBuffer is thread-safe and synchronized whereas StringBuilder is not, that’s why StringBuilder is faster than StringBuffer.

·         String concat + operator internally uses StringBuffer or StringBuilder class.

·         For String manipulations in a non-multi threaded environment, we should use StringBuilder else use StringBuffer class.

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