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.

Paul Rooney · Accepted Answer · 2018-06-18 05:12:00Z

159

Simply:

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

edited Jun 18, 2018 at 5:12

Paul Rooney

21.7k9 gold badges47 silver badges64 bronze badges

answered Sep 11, 2013 at 9:38

vahid kh

1,8822 gold badges12 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

lux Over a year ago

NPE is thrown if the Integer is null

dARKpRINCE Over a year ago

Works for int values.

luckyluke Over a year ago

Long.valueof should be used: stackoverflow.com/questions/2974561/new-integer-vs-valueof

Anonymous Over a year ago

This code works (Java implicitly unboxes the Integer to int and then casts to long before passing to the now deprecated Long(long) constructor.

Benjamin Zach Over a year ago

new Long is deprecated

Jon Skeet · Accepted Answer · 2011-07-14 08:59:44Z

108

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, 2011 at 8:59

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

5 Comments

Tiago Veloso Over a year ago

For arrays I can use a Number[] and a loop over it to create an appropriately typed array, right?

Jon Skeet Over a year ago

@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[].

MrMas Over a year ago

Why can't you cast from an Integer to a Long?

Jon Skeet Over a year ago

@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?

MrMas Over a year ago

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.

jelies · Accepted Answer · 2014-09-08 14:24:55Z

79

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 8, 2014 at 14:24

jelies

9,3106 gold badges52 silver badges65 bronze badges

answered Aug 9, 2013 at 15:34

Rich MacDonald

9356 silver badges5 bronze badges

1 Comment

Adrodoc Over a year ago

To be null save: Long l = i == null ? null : i.longValue()

Anon · Accepted Answer · 2012-07-26 02:50:17Z

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, 2012 at 2:50

Anon

2672 silver badges2 bronze badges

5 Comments

Bouncner Over a year ago

It makes absolutely no sense for me, but it works like a charm. Thanks a lot!

Jon Skeet Over a year ago

Introducing a string conversion for no reason is a really bad idea... there's simply no benefit in doing this.

depsypher Over a year ago

Agree with @JonSkeet, better off with this:Object i = 10;Long l = ((Number) i).longValue();

krispy Over a year ago

This method works fine but is relatively slow and uses more memory than the other methods of doing this...

ey dee ey em Over a year ago

looks great from a front end developer perspective

Paul Rooney · Accepted Answer · 2018-06-18 05:11:18Z

13

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, 2018 at 5:11

Paul Rooney

21.7k9 gold badges47 silver badges64 bronze badges

answered Jul 4, 2017 at 6:33

lostintranslation

5237 silver badges19 bronze badges

2 Comments

Andy Over a year ago

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.

lostintranslation Over a year ago

Integer is implicitly converted to a primitive long type.

Naresh Kumar · Accepted Answer · 2016-04-28 10:21:03Z

10

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();

answered Apr 28, 2016 at 10:21

Naresh Kumar

8149 silver badges25 bronze badges

Comments

Jeff Johny · Accepted Answer · 2015-04-17 07:09:07Z

6

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

Long i = 1234L;

answered Apr 17, 2015 at 7:09

Jeff Johny

4261 gold badge5 silver badges19 bronze badges

3 Comments

Diablo Over a year ago

I am sure you have answered without reading the entire question!

Dimitri W Over a year ago

@Diablo this question is the first result when searching "int to long" on Google, this answer may be useful to others

Diablo Over a year ago

@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.

max.kuzmentsov · Accepted Answer · 2016-08-02 18:15:35Z

5

((Number) intOrLongOrSomewhat).longValue()

answered Aug 2, 2016 at 18:15

max.kuzmentsov

7962 gold badges10 silver badges24 bronze badges

Comments

Steven Spungin · Accepted Answer · 2016-06-10 14:50:39Z

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, 2016 at 14:50

Steven Spungin

29.5k7 gold badges97 silver badges85 bronze badges

Comments

Pavlo Zvarych · Accepted Answer · 2016-06-15 12:38:53Z

2

new Long(Integer.longValue());

or

new Long(Integer.toString());

answered Jun 15, 2016 at 12:38

Pavlo Zvarych

6552 gold badges9 silver badges13 bronze badges

Comments

kaiser · Accepted Answer · 2020-07-28 09:31:20Z

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, 2020 at 9:31

kaiser

1,0391 gold badge15 silver badges30 bronze badges

Comments

Bremsstrahlung · Accepted Answer · 2017-03-29 15:48:28Z

1

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;
}

answered Mar 29, 2017 at 15:48

Bremsstrahlung

7401 gold badge10 silver badges24 bronze badges

Comments

Jin Kwon · Accepted Answer · 2021-03-30 03:28:16Z

1

For a nullable wrapper instance,

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

answered Mar 30, 2021 at 3:28

Jin Kwon

22.4k18 gold badges133 silver badges219 bronze badges

Comments

Shedrack · Accepted Answer · 2021-12-11 14:36:08Z

1

To convert Integer into Long simply cast the Integer value

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

answered Dec 11, 2021 at 14:36

Shedrack

7539 silver badges23 bronze badges

Comments

adkisson · Accepted Answer · 2018-09-25 07:30:38Z

0

This is null-safe

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

answered Sep 25, 2018 at 7:30

adkisson

4654 silver badges6 bronze badges

Comments

Joydeep Dutta · Accepted Answer · 2018-01-08 10:18:48Z

-4

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 8, 2018 at 10:18

answered Jan 8, 2018 at 9:52

Joydeep Dutta

32 bronze badges

Comments

Tiago Peres · Accepted Answer · 2020-01-31 15:44:15Z

-6

Try to convertValue by Jackson

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

edited Jan 31, 2020 at 15:44

Tiago Peres

15.9k22 gold badges104 silver badges174 bronze badges

answered Jan 31, 2020 at 15:17

lemonzone2010

1173 bronze badges

1 Comment

NickGreen Over a year ago

This is definitely not the best answer: this solution adds unnecessary complexity, performance overhead and requires an extra library (Jackson)

Collectives™ on Stack Overflow

Converting Integer to Long

17 Answers 17

5 Comments

5 Comments

1 Comment

5 Comments

2 Comments

Comments

3 Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

17 Answers 17

5 Comments

5 Comments

1 Comment

5 Comments

2 Comments

Comments

3 Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

1 Comment

Linked

Related