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final member

Posted on 2012-03-16
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Does declaring a class member as final cause it to take less memory or cause any processing using it to be faster?
same for final methods or classes?
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Question by:allelopath
8 Comments
 
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by:ksivananth
ID: 37729241
I don't think, final is nothing to do with memory/speed!
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by:ksivananth
ID: 37729243
*nothing - anything
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by:mccarl
mccarl earned 84 total points
ID: 37729320
The differences are probably very small, but yes there could be performance improvements. Any extra information you give the compiler, gives it a chance to optimize the bytecode more aggressively.

Essentially, because of this, but more importantly to help reduce bugs, you should use final everywhere where it is appropriate, it just gives the compiler more info and therefore more of a chance to pick up errors and to optimize.
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by:Kyle Abrahams
Kyle Abrahams earned 83 total points
ID: 37729348
It doesn't unless you are multithreading (making it visible to all threads, assigning only once) and for clearer design.

http://stackoverflow.com/questions/4279420/does-use-of-final-keyword-in-java-improve-the-performance
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Assisted Solution

by:gudii9
gudii9 earned 83 total points
ID: 37730900
Check following interesting explanation, link

Use private and static methods, and final classes, to encourage inlining by the compiler.

http://www.javaperformancetuning.com/tips/rawtips.shtml
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by:dpearson
dpearson earned 167 total points
ID: 37733629
For multi threaded code using final makes a huge difference in performance.  This isn't because of anything that's happening to the variable, it's because you don't need to lock the threads before you access the variable:

public class SlowClass {
    private int m_Value ;

    public synchronized int getValue() { return m_Value ; }
    public synchronized void setValue(int n) { m_Value = n ; }
}

public class FastClass {
    private final int m_Value ;

    public FastClass(int n) {
        m_Value = n ;
    }

    public int getValue() { return m_Value ; } // NOTE: Not synchronized
}

In a multi threaded situation SlowClass may run 100x slower than FastClass because there's no requirement to lock on the class before accessing the data.

This is when final really makes a difference.

It can also help the compiler produce slightly more optimized code (when applied to the class or member level) but those won't get you order of magnitude benefits, as the multi threading final will.

Doug
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by:ksivananth
ksivananth earned 83 total points
ID: 37736234
>>For multi threaded code using final makes a huge difference in performance

the diff is between sync/non-sync code, nothing to do with final.
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Accepted Solution

by:
dpearson earned 167 total points
ID: 37736264
>> the diff is between sync/non-sync code, nothing to do with final.

OK - technically correct it's not the "final" keyword that makes the performance difference, it's the different coding pattern that the use of final produces (i.e. immutable objects) which in turn generates the huge performance difference.

Doug
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