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Mistakes Made With String Object In Java:

Summary:

In this presentation we will discuss about the common mistakes made while using

String class object in a Java program.

Mistake 1:

This is a very common mistake to use '==' operator to compare the string objects

instead of '.equals' method. When two string objects are compared with '=='

operator, the result is true only if both the object references point to the single

object. This is called as a 'shallow comparison'. On the other hand, when two string

objects are compared with '.equals' method, the result will be dependent on the

actual string data of the objects and not on the references of the objects. This is

called as a 'deep comparison'.

Mistake 2:

JVM keeps a separate String literal pool for String objects. A common mistake

made while creating a string object is to use 'new' operator. Each time a new string

literal is created without using 'new' operator, JVM first checks if it is present in

the literal pool. If it is there, then the reference to the same is returned otherwise a

new literal is created in the same pool and its reference is returned. But when the

new literal is created using 'new' operator, the literal is allocated the memory

outside the string literal pool even if equal literal presents in the string literal pool.

The string literal pool is used to increase performance and decrease memory

overhead, so using the 'new' operator to create the string literal will not cause any

error to the logic but will increase the memory overhead. So better to use it only

when you know you need it.

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Mistake 3:

As we now know that string literals are stored in a separate literal pool, and two

objects with the same literal will point to the same memory of the literal pool, the

string objects are made immutable in Java. That means once the string object is

created its contents cannot be modified. So if you perform any string modification

operations on the string object, for each different result a new object will be

created in the pool. This ensures that if there are any other references to the string

then they will still point to the original string object and not the modified one. And

that is the reason we should avoid using String objects if we need to modify the

string data frequently. It is not the efficient way as it would create many strings

occupying the new storage area. In such a case we should use `StringBuffer' or

`StringBuilder' class.

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