<!DOCTYPE qhelp PUBLIC

"-//Semmle//qhelp//EN"

"qhelp.dtd">

<qhelp>

<overview>

<p>The <code>String</code> class is immutable, which means that there is

no way to change the string that it represents. Consequently, there is rarely a

need to copy a <code>String</code> object or construct a new instance based on

an existing string, for example by writing something like <code>String hello =

new String("hello")</code>. Furthermore, this practice is not memory efficient.</p>

</overview>

<recommendation>

<p>The copied string is functionally indistinguishable from the argument that

was passed into the <code>String</code> constructor, so you can simply omit the constructor call and

use the argument passed into it directly. Unless an explicit copy of the argument string is needed,

this is a safe transformation.</p>

</recommendation>

<example>

<p>The following example shows three cases of copying a string using the <code>String</code>

constructor, which is inefficient. In each case, simply removing the constructor call

<code>new String</code> and leaving the argument results in better code and less

memory churn.</p>

<sample src="NewStringString.java" />

</example>

<references>

<li>

J. Bloch, <em>Effective Java (second edition)</em>,

Item 5.

Addison-Wesley, 2008.

</li>

<li>

Java API Specification:

<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html#%3Cinit%3E(java.lang.String)">String(String)</a>.

</li>

</references>

</qhelp>