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.

Fuliginous

Answer 1

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...

Southeasterly

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

@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[]. – Southeasterly

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

@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? – Southeasterly

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. – Abdulabdulla

Answer 2

Simply:

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

Lyublin

NPE is thrown if the Integer is null – Unpremeditated

Works for int values. – Retrorse

Long.valueof should be used: https://mcmap.net/q/160531/-new-integer-vs-valueof – Francis

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

new Long is deprecated – Tryma

Answer 3

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.

Minor

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

Answer 4

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.

Pareira

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

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

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

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

looks great from a front end developer perspective – Untitled

Answer 5

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.

Pumice

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. – Allinclusive

Integer is implicitly converted to a primitive long type. – Pumice

Answer 6

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();

Thiamine

Answer 7

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

Long i = 1234L;

Dermal

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

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

@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. – Filtration

Answer 8

((Number) intOrLongOrSomewhat).longValue()

Lubber

Answer 9

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

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

Snath

Answer 10

new Long(Integer.longValue());

or

new Long(Integer.toString());

Dhahran

Answer 11

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();

Icky

Answer 12

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;
}

Yseulta

Answer 13

For a nullable wrapper instance,

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

Epos

Answer 14

To convert Integer into Long simply cast the Integer value

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

Kirbie

Answer 15

This is null-safe

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

Octoroon

Answer 16

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);

Carlicarlick

Answer 17

Try to convertValue by Jackson

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

Asthenosphere

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