Java correct way convert cast object to Double

Question

I need to convert Object o to Double  Is the correct way to convert it to String first

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If your Object represents a number  eg  such as an Integer  you can cast it to a Number then call the doubleValue   method   Double asDouble Object o        Double val   null      if  o instanceof Number            val     Number  o  doubleValue              return val

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Also worth mentioning -- if you were forced to use an older Java version prior to 1 5  and you are trying to use Collections  you won t be able to parameterize the collection with a type such as Double   You ll have to manually  box  to the class Double when adding new items  and  unbox  to the primitive double by parsing and casting  doing something like this    LinkedList lameOldList   new LinkedList    lameOldList add  new Double 1 2     lameOldList add  new Double 3 4     lameOldList add  new Double 5 6      double total   0 0  for  int i   0  len   lameOldList size    i  lt  len  i        total    Double valueOf   Double lameOldList get i          The old-school list will contain only type Object and so has to be cast to Double   Also  you won t be able to iterate through the list with an enhanced-for-loop in early Java versions -- only with a for-loop

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You can t cast an object to a Double if the object is not a Double   Check out the API   particularly note  valueOf double d    and  valueOf String s    Those methods give you a way of getting a Double instance from a String or double primitive    Also not the constructors  read the documentation to see how they work  The object you are trying to convert naturally has to give you something that can be transformed into a double   Finally  keep in mind that Double instances are immutable -- once created you can t change them

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Tried all these methods for conversion -         public static void main String   args         Object myObj   10 101      System out println  Cast to Double      Double myObj  10 99       concates      Double d1   new Double myObj toString         System out println  new Object String - Cast to Double     d1 10 99       works      double d3    double  myObj      System out println  new Object - Cast to Double     d3 10 99          works      double d4   Double valueOf  Double myObj       System out println  Double valueOf       d4 10 99             works      double d5     Number  myObj  doubleValue        System out println  Cast to Number and call doubleValue       d5 10 99            works      double d2  Double parseDouble  String  myObj       System out println  Cast to String to cast to Double     d2 10            works

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I tried this and it worked   Object obj   10  String str   obj toString     double d   Double valueOf str  doubleValue

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In Java version prior to 1 7 you cannot cast object to primitive type  double d    double  obj    You can cast an Object to a Double just fine  Double d    Double  obj    Beware  it can throw a ClassCastException if your object isn t a Double

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new Double object toString       But it seems weird to me that you re going from an Object to a Double  You should have a better idea what class of object you re starting with before attempting a conversion  You might have a bit of a code quality problem there   Note that this is a conversion  not casting

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You can use the instanceof operator to test to see if it is a double prior to casting  You can then safely cast it to a double  In addition you can test it against other known types  e g  Integer  and then coerce them into a double manually if desired       Double d   null      if  obj instanceof Double            d    Double  obj

[java] Java correct way convert/cast object to Double

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