Converting Integer to Long

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.

17 Answers

Simply:

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

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...

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.

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.

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.

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(); 

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

Long i = 1234L; 

((Number) intOrLongOrSomewhat).longValue() 

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

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

new Long(Integer.longValue()); 

or

new Long(Integer.toString()); 

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; } 

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(); 

For a nullable wrapper instance,

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

This is null-safe

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

To convert Integer into Long simply cast the Integer value

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

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); 

Try to convertValue by Jackson

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