Converting Integer to Long

user_166789 0
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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.

casting reflection java
17 Answers

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();
user_36049550

For a nullable wrapper instance,

Integer i;
Long l = Optional.ofNullable(i)
                 .map(Long::valueOf)
                 .orElse(null);
user_3304570

This is null-safe

Number tmp = getValueByReflection(inv.var1(), classUnderTest, runtimeInstance);
Long value1 = tmp == null ? null : tmp.longValue();
user_64021920

To convert Integer into Long simply cast the Integer value

Integer intValue = 23;
Long longValue = (long) intValue;
user_127331540

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);
user_91873220

Try to convertValue by Jackson

ObjectMapper mapper = new ObjectMapper()
Integer a = 1;
Long b = mapper.convertValue(a, Long.class)
user_89383650
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