How to convert a double to long without casting

Question

What is the best way to convert a double to a long without casting   For example   double d   394 000  long l    new Double d   longValue    System out println  double     d      long     l

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And here is the rounding way which doesn t truncate  Hurried to look it up in the Java API Manual   double d   1234 56  long x   Math round d     1235

User · Answer

Assuming you re happy with truncating towards zero  just cast   double d   1234 56  long x    long  d     x   1234   This will be faster than going via the wrapper classes - and more importantly  it s more readable  Now  if you need rounding other than  always towards zero  you ll need slightly more complicated code

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Simply put  casting is more efficient than creating a Double object

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If you have a strong suspicion that the DOUBLE is actually a LONG  and you want to  1  get a handle on its EXACT value as a LONG  2  throw an error when its not a LONG  you can try something like this   public class NumberUtils                  Convert a   link Double  to a   link Long         Method is for   link Double s that are actually   link Long s and we just       want to get a handle on it as one             public static long getDoubleAsLong double specifiedNumber            Assert isTrue NumberUtils isWhole specifiedNumber            Assert isTrue specifiedNumber  lt   Long MAX VALUE  amp  amp  specifiedNumber  gt   Long MIN VALUE              we already know its whole and in the Long range         return Double valueOf specifiedNumber  longValue               public static boolean isWhole double specifiedNumber               http   stackoverflow com questions 15963895 how-to-check-if-a-double-value-has-no-decimal-part         return  specifiedNumber   1    0             Long is a subset of Double  so you might get some strange results if you unknowingly try to convert a Double that is outside of Long s range    Test public void test   throws Exception          Confirm that LONG is a subset of DOUBLE  so numbers outside of the range can be problematic     Assert isTrue Long MAX VALUE  lt  Double MAX VALUE       Assert isTrue Long MIN VALUE  gt  -Double MAX VALUE      Not Double MIN VALUE   gt  read the Javadocs  Double MIN VALUE is the smallest POSITIVE double  not the bottom of the range of values that Double can possible be         Double longValue   failure due to being out of range   gt  results are the same even though I minus ten     System out println  Double valueOf Double MAX VALUE  longValue        Double valueOf Double MAX VALUE  longValue         System out println  Double valueOf Double MAX VALUE - 10  longValue        Double valueOf Double MAX VALUE - 10  longValue             casting failure due to being out of range   gt  results are the same even though I minus ten     System out println   long  Double valueOf Double MAX VALUE        long  Double valueOf Double MAX VALUE  doubleValue         System out println   long  Double valueOf Double MAX VALUE - 10  longValue         long  Double valueOf Double MAX VALUE - 10  doubleValue

User · Answer

new Double d   longValue   internally just does a cast  so there s no reason to create a Double object

User · Answer

Simply put  casting is more efficient than creating a Double object

User · Answer

And here is the rounding way which doesn t truncate  Hurried to look it up in the Java API Manual   double d   1234 56  long x   Math round d     1235

User · Answer

new Double d   longValue   internally just does a cast  so there s no reason to create a Double object

User · Answer

Simply put  casting is more efficient than creating a Double object

User · Answer

Simply by the following   double d   394 000  long l   d   1L

User · Answer

new Double d   longValue   internally just does a cast  so there s no reason to create a Double object

User · Answer

Assuming you re happy with truncating towards zero  just cast   double d   1234 56  long x    long  d     x   1234   This will be faster than going via the wrapper classes - and more importantly  it s more readable  Now  if you need rounding other than  always towards zero  you ll need slightly more complicated code

User · Answer

If you have a strong suspicion that the DOUBLE is actually a LONG  and you want to  1  get a handle on its EXACT value as a LONG  2  throw an error when its not a LONG  you can try something like this   public class NumberUtils                  Convert a   link Double  to a   link Long         Method is for   link Double s that are actually   link Long s and we just       want to get a handle on it as one             public static long getDoubleAsLong double specifiedNumber            Assert isTrue NumberUtils isWhole specifiedNumber            Assert isTrue specifiedNumber  lt   Long MAX VALUE  amp  amp  specifiedNumber  gt   Long MIN VALUE              we already know its whole and in the Long range         return Double valueOf specifiedNumber  longValue               public static boolean isWhole double specifiedNumber               http   stackoverflow com questions 15963895 how-to-check-if-a-double-value-has-no-decimal-part         return  specifiedNumber   1    0             Long is a subset of Double  so you might get some strange results if you unknowingly try to convert a Double that is outside of Long s range    Test public void test   throws Exception          Confirm that LONG is a subset of DOUBLE  so numbers outside of the range can be problematic     Assert isTrue Long MAX VALUE  lt  Double MAX VALUE       Assert isTrue Long MIN VALUE  gt  -Double MAX VALUE      Not Double MIN VALUE   gt  read the Javadocs  Double MIN VALUE is the smallest POSITIVE double  not the bottom of the range of values that Double can possible be         Double longValue   failure due to being out of range   gt  results are the same even though I minus ten     System out println  Double valueOf Double MAX VALUE  longValue        Double valueOf Double MAX VALUE  longValue         System out println  Double valueOf Double MAX VALUE - 10  longValue        Double valueOf Double MAX VALUE - 10  longValue             casting failure due to being out of range   gt  results are the same even though I minus ten     System out println   long  Double valueOf Double MAX VALUE        long  Double valueOf Double MAX VALUE  doubleValue         System out println   long  Double valueOf Double MAX VALUE - 10  longValue         long  Double valueOf Double MAX VALUE - 10  doubleValue

User · Answer

new Double d   longValue   internally just does a cast  so there s no reason to create a Double object

User · Answer

The preferred approach should be   Double valueOf d  longValue     From the Double  Java Platform SE 7  documentation   Double valueOf d       Returns a Double instance representing the specified double value    If a new Double instance is not required  this method should   generally be used in preference to the constructor Double double     as this method is likely to yield significantly better space and time   performance by caching frequently requested values

User · Answer

Guava Math library has a method specially designed for converting a double to a long   long DoubleMath roundToLong double x  RoundingMode mode    You can use java math RoundingMode to specify the rounding behavior

User · Answer

Simply by the following   double d   394 000  long l   d   1L

User · Answer

Assuming you re happy with truncating towards zero  just cast   double d   1234 56  long x    long  d     x   1234   This will be faster than going via the wrapper classes - and more importantly  it s more readable  Now  if you need rounding other than  always towards zero  you ll need slightly more complicated code

User · Answer

And here is the rounding way which doesn t truncate  Hurried to look it up in the Java API Manual   double d   1234 56  long x   Math round d     1235

User · Answer

Assuming you re happy with truncating towards zero  just cast   double d   1234 56  long x    long  d     x   1234   This will be faster than going via the wrapper classes - and more importantly  it s more readable  Now  if you need rounding other than  always towards zero  you ll need slightly more complicated code

User · Answer

Guava Math library has a method specially designed for converting a double to a long   long DoubleMath roundToLong double x  RoundingMode mode    You can use java math RoundingMode to specify the rounding behavior

User · Answer

Simply put  casting is more efficient than creating a Double object

User · Answer

The preferred approach should be   Double valueOf d  longValue     From the Double  Java Platform SE 7  documentation   Double valueOf d       Returns a Double instance representing the specified double value    If a new Double instance is not required  this method should   generally be used in preference to the constructor Double double     as this method is likely to yield significantly better space and time   performance by caching frequently requested values

User · Answer

And here is the rounding way which doesn t truncate  Hurried to look it up in the Java API Manual   double d   1234 56  long x   Math round d     1235

[java] How to convert a double to long without casting?

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