Converting Integer to Long

Question

I need to get the value of a field using reflection. It so happens that I am not always sure what the datatype of the field is. For that, and to avoid some code duplication I have created the following method:

@SuppressWarnings("unchecked")
private static <T> T getValueByReflection(VarInfo var, Class<?> classUnderTest, Object runtimeInstance) throws Throwable {
  Field f = classUnderTest.getDeclaredField(processFieldName(var));
  f.setAccessible(true);
  T value = (T) f.get(runtimeInstance);

  return value;
}

And use this method like:

Long value1 = getValueByReflection(inv.var1(), classUnderTest, runtimeInstance);

or

Double[] value2 = getValueByReflection(inv.var2(), classUnderTest, runtimeInstance);

The problem is that I can't seem to cast Integer to Long:

java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Long

Is there a better way to achieve this?

I am using Java 1.6.

score 159 · Answer 1 · edited Jun 18 '18 at 05:12

159

Simply:

Integer i = 7;
Long l = new Long(i);

edited Jun 18 '18 at 05:12

Paul Rooney

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answered Sep 11 '13 at 09:38

vahid kh

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18

NPE is thrown if the Integer is null – lux Feb 02 '15 at 22:16
2

Works for `int` values. – dARKpRINCE Aug 06 '15 at 14:26
24

Long.valueof should be used: http://stackoverflow.com/questions/2974561/new-integer-vs-valueof – luckyluke Aug 23 '16 at 08:59
1

This code works (Java implicitly unboxes the `Integer` to `int` and then casts to `long` before passing to the now deprecated `Long(long)` constructor. – Ole V.V. Oct 01 '18 at 12:53
2

`new Long` is deprecated – Benjamin Zach Jan 19 '22 at 09:31

score 109 · Accepted Answer · answered Jul 14 '11 at 08:59

109

No, you can't cast Integer to Long, even though you can convert from int to long. For an individual value which is known to be a number and you want to get the long value, you could use:

Number tmp = getValueByReflection(inv.var1(), classUnderTest, runtimeInstance);
Long value1 = tmp.longValue();

For arrays, it will be trickier...

answered Jul 14 '11 at 08:59

Jon Skeet

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For arrays I can use a `Number[]` and a loop over it to create an appropriately typed array, right? – Tiago Veloso Jul 14 '11 at 09:39
@Tiago: It depends on what the method's *actually* returning. That wouldn't work for a `double[]` for example, but *would* work for a `Double[]`. – Jon Skeet Jul 14 '11 at 09:40
8

Why can't you cast from an Integer to a Long? – MrMas Mar 26 '13 at 22:26
@MrMas: Because they're separate reference types, both direct subclasses of `Number`. Or to put it another way: which conversion rule do you believe *does* let you convert from one to the other? – Jon Skeet Mar 27 '13 at 06:44
7

Ok. The problem is inheritance. I'm thinking in terms of precision. An integer can be converted to a long integer without losing information. But the inheritance structure doesn't have any information that would tell the compiler that. – MrMas Mar 27 '13 at 13:50

score 75 · Answer 3 · edited Sep 08 '14 at 14:24

75

Integer i = 5; //example

Long l = Long.valueOf(i.longValue());

This avoids the performance hit of converting to a String. The longValue() method in Integer is just a cast of the int value. The Long.valueOf() method gives the vm a chance to use a cached value.

edited Sep 08 '14 at 14:24

jelies

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answered Aug 09 '13 at 15:34

Rich MacDonald

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5

To be null save: Long l = i == null ? null : i.longValue() – Adrodoc Sep 30 '16 at 10:27

score 21 · Answer 4 · answered Jul 26 '12 at 02:50

21

Oddly enough I found that if you parse from a string it works.

 int i = 0;
 Long l = Long.parseLong(String.valueOf(i));
 int back = Integer.parseInt(String.valueOf(l));

Win.

answered Jul 26 '12 at 02:50

Anon

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It makes absolutely no sense for me, but it works like a charm. Thanks a lot! – Bouncner Jan 31 '13 at 23:08
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Introducing a string conversion for no reason is a really bad idea... there's simply no benefit in doing this. – Jon Skeet Mar 27 '13 at 13:53
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Agree with @JonSkeet, better off with this:Object i = 10;Long l = ((Number) i).longValue(); – depsypher Jun 19 '13 at 20:02
1

This method works fine but is relatively slow and uses more memory than the other methods of doing this... – krispy Feb 27 '14 at 21:55
2

looks great from a front end developer perspective – ey dee ey em Jan 19 '18 at 19:27

score 12 · Answer 5 · edited Jun 18 '18 at 05:11

12

If the Integer is not null

Integer i;
Long long = Long.valueOf(i);

i will be automatically typecast to a long.

Using valueOf instead of new allows caching of this value (if its small) by the compiler or JVM , resulting in faster code.

edited Jun 18 '18 at 05:11

Paul Rooney

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answered Jul 04 '17 at 06:33

lostintranslation

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I can't find a Long.valueOf(Integer i) method, the only ones I find are valueOf(long l), valueOf(String s) and valueOf(String s, int radix). Checked for Java8 and Java9 docs. – Andy Jan 10 '18 at 23:20
3

Integer is implicitly converted to a primitive long type. – lostintranslation Jan 16 '18 at 05:41

score 10 · Answer 6 · answered Apr 28 '16 at 10:21

Converting Integer to Long Very Simple and many ways to converting that
Example 1

 new Long(your_integer);

Example 2

Long.valueOf(your_integer);

Example 3

Long a = 12345L;

Example 4
If you already have the int typed as an Integer you can do this:

Integer y = 12;
long x = y.longValue();

score 7 · Answer 7 · answered Apr 17 '15 at 07:09

7

Convert an integer directly to long by adding 'L' to the end of Integer.

Long i = 1234L;

answered Apr 17 '15 at 07:09

Jeff Johny

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I am sure you have answered without reading the entire question! – Diablo Mar 24 '16 at 12:06
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@Diablo this question is the first result when searching "int to long" on Google, this answer may be useful to others – Dimitri W Oct 08 '16 at 23:20
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@DimitriW I am not saying this answer is wrong, But I am saying the answer for this question is wrong. You are right,This is useful for those people who doesn't read the question and look at the answer only. – Diablo Oct 25 '16 at 08:55

score 5 · Answer 8 · answered Aug 02 '16 at 18:15

5

((Number) intOrLongOrSomewhat).longValue()

answered Aug 02 '16 at 18:15

max.kuzmentsov

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score 2 · Answer 9 · answered Jun 10 '16 at 14:50

2

If you know that the Integer is not NULL, you can simply do this:

Integer intVal = 1;
Long longVal = (long) (int) intVal

answered Jun 10 '16 at 14:50

Steven Spungin

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score 2 · Answer 10 · answered Jun 15 '16 at 12:38

2

new Long(Integer.longValue());

or

new Long(Integer.toString());

answered Jun 15 '16 at 12:38

Pavlo Zvarych

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score 2 · Answer 11 · answered Jul 28 '20 at 09:31

2

If you don't know the exact class of your number (Integer, Long, Double, whatever), you can cast to Number and get your long value from it:

Object num = new Integer(6);
Long longValue = ((Number) num).longValue();

answered Jul 28 '20 at 09:31

kaiser

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score 1 · Answer 12 · answered Mar 29 '17 at 15:48

A parser from int variables to the long type is included in the Integer class. Here is an example:

int n=10;
long n_long=Integer.toUnsignedLong(n);

You can easily use this in-built function to create a method that parses from int to long:

    public static long toLong(int i){
    long l;
    if (i<0){
        l=-Integer.toUnsignedLong(Math.abs(i));
    }
    else{
        l=Integer.toUnsignedLong(i);
    }
    return l;
}

score 1 · Answer 13 · answered Mar 30 '21 at 03:28

1

For a nullable wrapper instance,

Integer i;
Long l = Optional.ofNullable(i)
                 .map(Long::valueOf)
                 .orElse(null);

answered Mar 30 '21 at 03:28

Jin Kwon

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score 1 · Answer 14 · answered Dec 11 '21 at 14:36

1

To convert Integer into Long simply cast the Integer value

Integer intValue = 23;
Long longValue = (long) intValue;

answered Dec 11 '21 at 14:36

Shedrack

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score 0 · Answer 15 · answered Sep 25 '18 at 07:30

0

This is null-safe

Number tmp = getValueByReflection(inv.var1(), classUnderTest, runtimeInstance);
Long value1 = tmp == null ? null : tmp.longValue();

answered Sep 25 '18 at 07:30

adkisson

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Joydeep Dutta · Answer 16 · 2018-01-08T10:18:48.117

-3

In case of a List of type Long, Adding L to end of each Integer value

List<Long> list = new ArrayList<Long>();
list  = Arrays.asList(1L, 2L, 3L, 4L);

edited Jan 08 '18 at 10:18

answered Jan 08 '18 at 09:52

Joydeep Dutta

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score -4 · Answer 17 · edited Jan 31 '20 at 15:44

-4

Try to convertValue by Jackson

ObjectMapper mapper = new ObjectMapper()
Integer a = 1;
Long b = mapper.convertValue(a, Long.class)

edited Jan 31 '20 at 15:44

Tiago Martins Peres

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answered Jan 31 '20 at 15:17

lemonzone2010

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This is definitely not the best answer: this solution adds unnecessary complexity, performance overhead and requires an extra library (Jackson) – NickGreen May 20 '20 at 12:34

Converting Integer to Long

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