Difference between Long.parseLong(String s) and new Long(String s)?

Question

I know that the String can be converted to a long using Long.parseLong(String) method and Long(String) constructor.

String str="12356";
Long myvar= Long.parseLong(str);
Long myvar2 = new Long(str);

Both of them gives same output. Value of myvar and myvar2 is same. I would like to know which one gives better performance and when to use parseLong and when to use new Long(String s).

Did you meant `Long.parseLong` ? Otherwise, that wouldn't compile. — Alexis C., Jan 02 '14 at 08:21
@ZouZou: Thanks for pointing that out it was a typo. Fixed it. — Chaitanya, Jan 02 '14 at 08:25
Do you really mean to box the result of `Long.parseLong`? it does not return `Long` — Sean Owen, Jan 02 '14 at 08:25

score 7 · Answer 1 · edited Jan 02 '14 at 08:31

7

The difference is

parseLong returns a primitive
new Long() will always create a new objecct

edited Jan 02 '14 at 08:31

yshavit

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answered Jan 02 '14 at 08:23

Prasad Kharkar

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score 5 · Accepted Answer · answered Jan 02 '14 at 08:19

5

new Long will always create a new object, whereas parseLong doesn't.

I advise you to go through the implementation of each one.

answered Jan 02 '14 at 08:19

Maroun

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score 0 · Answer 3 · answered Jan 02 '14 at 08:19

0

If you open look at Long.java source, you can see that Long(String) actually calls parseLong(String).

The only difference is creating a new Long object. Therefore if you ignore object creation cost, they give same performance.

answered Jan 02 '14 at 08:19

Amila

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score 0 · Answer 4 · answered Jan 02 '14 at 08:23

0

The constructor (new Long(String)) calls immediately Long.parseLong(String) method. So, if you use parseLong() you will omit an extra call. However, they will give a similar performance actually.

The source of Java:

public Long(String s) throws NumberFormatException {
    this.value = parseLong(s, 10);
}

answered Jan 02 '14 at 08:23

ovunccetin

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... except that you have also created a new object. – Sean Owen Jan 02 '14 at 08:24

score 0 · Answer 5 · answered Jan 02 '14 at 08:47

0

If the question really means Long myvar = Long.parseLong(str) then these are in fact identical in performance, because this line also contains a new Long creation via boxing. parseLong() is called in both cases, and a new Long is created with its field assigned.

If the intent was to create a long instead, which is more likely, then parseLong() is better and marginally faster for avoiding a pointless object creation.

answered Jan 02 '14 at 08:47

Sean Owen

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Autoboxing uses valueOf() -> http://stackoverflow.com/questions/408661/what-code-does-the-compiler-generate-for-autoboxing – Svetlin Zarev Jan 02 '14 at 08:49
Uses `valueOf(long)`, yes. My point is that either way you have all but identical operations: `new Long` which does `this.value = value`, and a call to `parseLong`. – Sean Owen Jan 02 '14 at 09:26
... although if you're getting at the fact that `valueOf(long)` caches -128L to 127L, yeah that would be a difference and slight reason to prefer the boxing. – Sean Owen Jan 02 '14 at 09:28

Difference between Long.parseLong(String s) and new Long(String s)?

5 Answers5