How do I convert from int to Long in Java?

Question

I keep finding both on here and Google people having troubles going from long to int and not the other way around. Yet I'm sure I'm not the only one that has run into this scenario before going from int to Long.

The only other answers I've found were "Just set it as Long in the first place" which really doesn't address the question.

I initially tried casting but I get a "Cannot cast from int to Long"

for (int i = 0; i < myArrayList.size(); ++i ) {
    content = new Content();
    content.setDescription(myArrayList.get(i));
    content.setSequence((Long) i);
    session.save(content);
}

As you can imagine I'm a little perplexed, I'm stuck using int since some content is coming in as an ArrayList and the entity for which I'm storing this info requires the sequence number as a Long.

Zetes

for (long i = 0; i < myList.size(); ++i) works too – Dunc

@Dunc Yes that will work for the loop, but as I specified at the bottom of my question the ArrayList I'm working with requires the primitive int when specifying what index position to get – Zetes

long longValue = intValue | 0L; – Liverpudlian

What I did is: cast int to long first, then assign long to Long. e.g int x = 2; Long y = (long)x; – Wafer

Answer 1

Note that there is a difference between a cast to long and a cast to Long. If you cast to long (a primitive value) then it should be automatically boxed to a Long (the reference type that wraps it).

You could alternatively use new to create an instance of Long, initializing it with the int value.

Stole

To demonstrate what Earwicker said you could call Long.valueOf(i), which takes a long but will widen an int and give you back a Long object. – Donley

Autoboxing is preferable, because it doesn't necessarily have to create a new Long object every time. – Benitez

(Warning: the rest of this comment is guesswork and conjecture) If the values given to Long.valueOf() fall between 0 and 128, which is very common, and it returns a cached instance, will that be preferable over autoboxing? (I may ask a new question if you think it's worth it...) – Donley

Autoboxing does the same thing as that. By the way, it's between -127 and 128. – Stole

@Grundlefleck: Autoboxing uses Long.valueOf() (if I remember correctly), so there wouldn't be a difference at all. My comment was in reply to the answer, not to your comment. – Benitez

And watch out for accidentally writing a == b to compare two boxed values! Will appear to work if they're in the "interning" range, will fail if not. And the range is a minimum of -128 to 127, but may be larger. (I think that's right, looks like I typed it the wrong way round in my last comment). – Stole

@mmyers: ah I see, cheers. @Earwicker: may I be so bold to suggest there's some information in these comments that would earn your answer at least another +1 were it to be included? :-) – Donley

@Donley - thanks, but would probably make more sense on a question about what autoboxing is equivalent to, e.g. you could upvote this answer: #766968 – Stole

Answer 2

Use the following: Long.valueOf(int);.

Heeltap

Look out, as this will generate a NullPointerException if you are receiving a Integer object which is null. – Palingenesis

correct if am wron i thought may be the answer is old becuse i cant find the method Long.valueOf(int) !! – Amenity

@Palingenesis - a primitive 'int' variable cannot be null. – Advice

@Amenity - see serg's comment - but I think this method casts the int to a long which autoboxes with a Long... so seems redundant – Advice

@Advice an Integer can, which is what he said. – Chevrotain

@1blustone either way, it is a red herring: if an Integer was received then a nullpointer would not be generated by this call but by the attempt to get the number into the required primitive: long (Long.valueOf(int) doesn't exists) – Advice

There is no such method in Java, you mistook it for Long.valueOf(long) – Whiting

Answer 3

If you already have the int typed as an Integer you can do this:

Integer y = 1;
long x = y.longValue();

Anagoge

Answer 4

use

new Long(your_integer);

or

Long.valueOf(your_integer);

Gristede

Answer 5

 1,new Long(intValue);
 2,Long.valueOf(intValue);

Carbamidine

For anyone trying now, Long.valueOf(intValue) is the way to go and constructor approach is deprecated. – Formfitting

Answer 6

How About

int myInt = 88;

// Will not compile

Long myLong = myInt;

// Compiles, and retains the non-NULL spirit of int. The best cast is no cast at all. Of course, your use case may require Long and possible NULL values. But if the int, or other longs are your only input, and your method can be modified, I would suggest this approach.

long myLong = myInt;

// Compiles, is the most efficient way, and makes it clear that the source value, is and will never be NULL.

Long myLong = (long) myInt;

Sherbrooke

Answer 7

In Java you can do:

 int myInt=4;
 Long myLong= new Long(myInt);

in your case it would be:

content.setSequence(new Long(i));

Offset

Answer 8

I have this little toy, that also deals with non generic interfaces. I'm OK with it throwing a ClassCastException if feed wrong (OK and happy)

public class TypeUtil {
    public static long castToLong(Object o) {
        Number n = (Number) o;
        return n.longValue();
    }
}

Gonad

Answer 9

We shall get the long value by using Number reference.

public static long toLong(Number number){
    return number.longValue();
}

It works for all number types, here is a test:

public static void testToLong() throws Exception {
    assertEquals(0l, toLong(0));   // an int
    assertEquals(0l, toLong((short)0)); // a short
    assertEquals(0l, toLong(0l)); // a long
    assertEquals(0l, toLong((long) 0)); // another long
    assertEquals(0l, toLong(0.0f));  // a float
    assertEquals(0l, toLong(0.0));  // a double

}

Hokusai

Answer 10

I had a great deal of trouble with this. I just wanted to:

thisBill.IntervalCount = jPaidCountSpinner.getValue();

Where IntervalCount is a Long, and the JSpinner was set to return a Long. Eventually I had to write this function:

    public static final Long getLong(Object obj) throws IllegalArgumentException {
    Long rv;

    if((obj.getClass() == Integer.class) || (obj.getClass() == Long.class) || (obj.getClass() == Double.class)) {
        rv = Long.parseLong(obj.toString());
    }
    else if((obj.getClass() == int.class) || (obj.getClass() == long.class) || (obj.getClass() == double.class)) {
        rv = (Long) obj;
    }
    else if(obj.getClass() == String.class) {
        rv = Long.parseLong(obj.toString());
    }
    else {
        throw new IllegalArgumentException("getLong: type " + obj.getClass() + " = \"" + obj.toString() + "\" unaccounted for");
    }

    return rv;
}

which seems to do the trick. No amount of simple casting, none of the above solutions worked for me. Very frustrating.

Nostradamus

if jPaidCountSpinner.getValue() returns an Object that is in fact a Long, you definitely only need to put a (Long) cast in front. Also try putting a breakpoint on your check for int.class or long.class etc. Does it ever hit it? And if you have a number-like object, it will support java.util.Number, so cast it to that and call the longValue method. No need to go via a string in that case. So this function could be simplified quite a bit, even if you also need to deal with strings. (Part of the problem here is the bad reference documentation for JSpinner). – Stole

I too ended up doing something like this. I wasn't sure what kind of number I would receive and was willing to convert it to Long with little concern for efficiency but wanting to avoid boilerplate. – Pansy

Answer 11

 //Suppose you have int and you wan to convert it to Long
 int i=78;
 //convert to Long
 Long l=Long.valueOf(i)

Chalaza

Answer 12

Suggested From Android Studio lint check : Remove Unnecessary boxing : So, unboxing is :

public  static  long  integerToLong (int minute ){
    int delay = minute*1000;
    long diff = (long) delay;
    return  diff ; 
}

Braunite

Answer 13

Apart from the other ways suggested here, one can try the below code as well.

(long)intValue

primitive to primitive.

Proprietress

Answer 14

As soon as there is only method Long.valueOf(long), cast from int to long will be done implicitly in case of using Long.valueOf(intValue).

The more clear way to do this is

Integer.valueOf(intValue).longValue()

Ruthenium

longValue is just a (long), so the only thing you "gain" here is Integer's internal cache. – Degrease

yeah. how about just (long) intValue ? – Silvanus