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  lt T gt  T getValueByReflection VarInfo var  Class lt   gt  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

User · Answer

If you know that the Integer is not NULL  you can simply do this   Integer intVal   1  Long longVal    long   int  intVal

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This is null-safe  Number tmp   getValueByReflection inv var1    classUnderTest  runtimeInstance   Long value1   tmp    null   null   tmp longValue

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Convert an integer directly to long by adding  L  to the end of Integer   Long i   1234L

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Number  intOrLongOrSomewhat  longValue

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Try to convertValue by Jackson  ObjectMapper mapper   new ObjectMapper   Integer a   1  Long b   mapper convertValue a  Long class

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Simply   Integer i   7  Long l   new Long i

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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

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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

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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

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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

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In case of a List of type Long   Adding L to end of each Integer value   List lt Long gt  list   new ArrayList lt Long gt     list    Arrays asList 1L  2L  3L  4L

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new Long Integer longValue       or      new Long Integer toString

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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

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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 lt 0           l -Integer toUnsignedLong Math abs i              else          l Integer toUnsignedLong i             return l

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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

[java] Converting Integer to Long

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