How do you know a variable type in java

Question

Let s say I declare a variable   String a    test     And I want to know what type it is  i e   the output should be java lang String How do I do this

User · Accepted Answer

a getClass   getName

User · Answer

I agree with what Joachim Sauer said  not possible to know  the variable type  not value type   unless your variable is a class attribute  and you would have to retrieve class fields  get the right field by name      Actually for me it s totally impossible that any a xxx   yyy   method give you the right answer since the answer would be different on the exact same object  according to the context in which you call this method     As teehoo said  if you know at compile a defined list of types to test you can use instanceof but you will also get subclasses returning true      One possible solution would also be to inspire yourself from the implementation of java lang reflect Field and create your own Field class  and then declare all your local variables as this custom Field implementation    but you d better find another solution  i really wonder why you need the variable type  and not just the value type

User · Answer

I learned from the Search Engine My English is very bad   So code     How to get variable s type  Up s    String str    test   String type   str getClass   getName    value  type   java lang String   this method    str getClass   getSimpleName    value String   now example   Object o   1  o getClass   getSimpleName    value Integer

User · Answer

Use operator overloading feature of java  class Test        void printType String x            System out print  String               void printType int x                 System out print  Int                  same goes on with boolean double float object

User · Answer

I think we have multiple solutions here    instance of could be a solution    Why  In Java every class is inherited from the Object class itself  So if you have a variable and you would like to know its type  You can use   System out println   Object f  getClass   getName       or   Integer class isInstance 1985      gives true   or   isPrimitive    public static void main String   args      ClassDemo classOne   new ClassDemo     Class classOneClass   classOne      int i   5   Class iClass   int class       checking for primitive type  boolean retval1   classOneClass isPrimitive     System out println  classOneClass is primitive type        retval1        checking for primitive type   boolean retval2   iClass isPrimitive     System out println  iClass is primitive type        retval2        This going to give us    FALSE TRUE   Find out more here  How to determine the primitive type of a primitive variable   https   docs oracle com javase tutorial java nutsandbolts datatypes html  http   docs oracle com cd E26806 01 wlp 1034 e14255 com bea p13n expression operator Instanceof html

User · Answer

I would like to expand on Martin s answer there     His solution is rather nice  but it can be tweaked so any  variable type  can be printed like that  It s actually Value Type  more on the topic   That said   tweaked  may be a strong word for this  Regardless  it may be helpful   Martins Solution   a getClass   getName     However  If you want it to work with anything you can do this     Object  myVar  getClass   getName     OR   Object  myInt  getClass   getSimpleName     In this case  the primitive will simply be wrapped in a Wrapper  You will get the Object of the primitive in that case   I myself used it like this   private static String nameOf Object o        return o getClass   getSimpleName        Using Generics   public static  lt T gt  String nameOf T o        return o getClass   getSimpleName

User · Answer

If you want the name  use Martin s method  If you want to know whether it s an instance of a certain class   boolean b   a instanceof String

[java] How do you know a variable type in java?

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