Different between parseInt() and valueOf() in java?

Question

How is parseInt() different from valueOf() ?

They appear to do exactly the same thing to me (also goes for parseFloat(), parseDouble(), parseLong() etc, how are they different from Long.valueOf(string) ?

Also, which one of these is preferable and used more often by convention?

Solution 1

Well, the API for Integer.valueOf(String) does indeed say that the String is interpreted exactly as if it were given to Integer.parseInt(String). However, valueOf(String) returns a new Integer() object whereas parseInt(String) returns a primitive int.

If you want to enjoy the potential caching benefits of Integer.valueOf(int), you could also use this eyesore:

Integer k = Integer.valueOf(Integer.parseInt("123"))

Now, if what you want is the object and not the primitive, then using valueOf(String) may be more attractive than making a new object out of parseInt(String) because the former is consistently present across Integer, Long, Double, etc.

Solution 2

From this forum:

parseInt() returns primitive integer type (int), whereby valueOf returns java.lang.Integer, which is the object representative of the integer. There are circumstances where you might want an Integer object, instead of primitive type.

Of course, another obvious difference is that intValue is an instance method whereby parseInt is a static method.

Solution 3

Integer.valueOf(s)

is similar to

new Integer(Integer.parseInt(s))

The difference is valueOf() returns an Integer, and parseInt() returns an int (a primitive type). Also note that valueOf() can return a cached Integer instance, which can cause confusing results where the result of == tests seem intermittently correct. Before autoboxing there could be a difference in convenience, after java 1.5 it doesn't really matter.

Moreover, Integer.parseInt(s) can take primitive datatype as well.

Solution 4

Look at Java sources: valueOf is using parseInt :

/**
 * Parses the specified string as a signed decimal integer value.
 *
 * @param string
 *            the string representation of an integer value.
 * @return an {@code Integer} instance containing the integer value
 *         represented by {@code string}.
 * @throws NumberFormatException
 *             if {@code string} cannot be parsed as an integer value.
 * @see #parseInt(String)
 */
public static Integer valueOf(String string) throws NumberFormatException {
    return valueOf(parseInt(string));
}

parseInt returns int (not Integer)

/**
 * Parses the specified string as a signed decimal integer value. The ASCII
 * character \u002d ('-') is recognized as the minus sign.
 *
 * @param string
 *            the string representation of an integer value.
 * @return the primitive integer value represented by {@code string}.
 * @throws NumberFormatException
 *             if {@code string} cannot be parsed as an integer value.
 */
public static int parseInt(String string) throws NumberFormatException {
    return parseInt(string, 10);
}

Solution 5

Integer.parseInt can just return int as native type.

Integer.valueOf may actually need to allocate an Integer object, unless that integer happens to be one of the preallocated ones. This costs more.

If you need just native type, use parseInt. If you need an object, use valueOf.

Also, because of this potential allocation, autoboxing isn't actually good thing in every way. It can slow down things.

View more solutions

Comments

[Adam Rosenfield]

valueOf() can return the same object for successive calls with the same argument (and is required to for arguments between -128 and 127 inclusive). new Integer() will always create a new object.

[gregory boero.teyssier]

Which one is used more often? Which one should I use the most?

[Anne Porosoff]

Worth mentioning: valueOf versions will also use an internal reference pool to return the SAME object for a given value, not just another instance with the same internal value. This means that given two Longs returned in this way, a.equals(b) == true and a == b is true

[palantus]

Actually, not quite true. I thought so myself at first, but the Javadocs for Integer.valueOf(String) clearly state that it is equivalent to new Integer(Integer.parseInt(String)). Integer.valueOf(int) does indeed cache, though.

[OscarRyz]

@bassezero. Also, that pool has a limit. I think it was -127 to 127.

[Donal Fellows]

The size of the reference pool is a true example of an implementation detail; it could even be increased in size in a patch release, and you should never rely on it for anything.

[Logan]

Is there any Performance or Memory difference between the two approaches?

[Thomas Eding]

Integer.valueOf(Integer.parseInt("123")) has no benefit over Integer.valueOf("123") or Integer.valueOf(123) aside from wasting cycles and the size of your program.

[foo]

There is a difference - the new Object (potentially) allocated by valueOf comes with an overhead (memory for the object, handling, GC), while the plain int is extremely "lightweight". (For the most common values, you'll get references to pre-existing Objects, which helps a tiny bit.)

[Holger]

Integer.valueOf(String) does exactly the same caching as Integer.valueOf(int). In fact, it is implemented as Integer.valueOf(Integer.parseInt(…)) …

[Khez]

At least in Java 1.8.0, Integer.valueOf(123) returns the primitive int. Testing showed that between [-127, 128] it returns the primitive not the object, which is exactly a signed byte.

[user207421]

@Khez It is impossible for it to return a primitive int. The signature says it returns an Integer, and that is exactly what it does. This answer is also partially incorrect when it says it returns a 'new' Integer. That's not what it says in the Javadoc. It is free to return a cached Integer.

[Jean-François Savard]

@OscarRyz Actually it's -128 to 127. Note that JVM offer a parameter to set the highest bound higher for the cache. However, you can't re-define the lowest bound : stackoverflow.com/questions/29633158/…

[Simon Forsberg]

No one has mentioned intValue, why does your answer mentions intValue?

[Ciro Santilli OurBigBook.com]

Documentation bug. Love it.

[MC Emperor]

"valueOf(String) returns a new Integer() object" — Not entirely. At least in the Integer class implementation in Java 8, Integers with a value between -128 and 127 are cached. Integer.valueOf("42") == Integer.valueOf("42") returns true.

[Zoe stands with Ukraine]

Please don't abuse bold formatting: it degrades the readability of your post.

[kaya3]

Integer k = Integer.valueOf(Integer.parseInt("123")); is equivalent to Integer k = Integer.parseInt("123"); because autoboxing is done by calling Integer.valueOf anyway. But as noted, Integer.valueOf(String) does use the cache too.

[Pratik]

@Joan d Silva from your last line, I think Integer.parseInt(s) can only take as an String whereas Integer.ValueOf(s) can take both int and string as an input argument

[Torben]

@basszero This is no longer true. At least since Java 8, the Integer.valueOf(String) simply combines Integer.parseInt(String) and Integer.valueOf(int).