Java: how to determine type of object in an array of objects?

Question

Example:

Object[] x = new Object[2];
x[0] = 3; // integer
x[1] = "4"; // String
System.out.println(x[0].getClass().getSimpleName()); // prints "Integer"
System.out.println(x[1].getClass().getSimpleName()); // prints "String"

This makes me wonder: the first object element is an instance of class Integer? or is it a primitive data type int? There is a difference, right?

So if I want to determine the type of first element (is it an integer, double, string, etc), how to do that? Do I use x[0].getClass().isInstance()? (if yes, how?), or do I use something else?

biziclop · Accepted Answer · 2011-02-11 00:24:18Z

6

There is a difference between int and Integer and only an Integer can go into an Object [] but autoboxing/unboxing makes it hard to pin it down.

Once you put your value in the array, it is converted to Integer and its origins are forgotten. Likewise, if you declare an int [] and put an Integer into it, it is converted into an int on the spot and no trace of it ever having been an Integer is preserved.

answered Feb 11, 2011 at 0:24

biziclop

50k12 gold badges80 silver badges108 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

irreputable · Accepted Answer · 2011-02-11 01:03:40Z

6

not what you asked, but if anyone wants to determine the type of allowed objects in an array:

 Oject[] x = ...; // could be Object[], int[], Integer[], String[], Anything[]

 Class classT = x.getClass().getComponentType();

answered Feb 11, 2011 at 1:03

irreputable

45.6k9 gold badges69 silver badges94 bronze badges

Comments

Lucas Zamboulis · Accepted Answer · 2014-06-07 12:55:02Z

6

x is an object array - so it can't contain primitives, only objects, and therefore the first element is of type Integer. It becomes an Integer by autoboxing, as @biziclop said

To check the type of a variable, use instanceof:

if (x[0] instanceof Integer) 
   System.out.println(x[0] + " is of type Integer")

edited Jun 7, 2014 at 12:55

answered Feb 11, 2011 at 0:25

Lucas Zamboulis

2,5515 gold badges24 silver badges28 bronze badges

Comments

jluzwick · Accepted Answer · 2011-02-11 00:27:31Z

4

You want to use the instanceof operator.

for instance:

if(x[0] instanceof Integer) {
 Integer anInt = (Integer)x[0];
 // do this
} else if(x[0] instanceof String) {
 String aString = (String)x[0];
 //do this
}

answered Feb 11, 2011 at 0:27

jluzwick

2,0352 gold badges16 silver badges24 bronze badges

Collectives™ on Stack Overflow

Java: how to determine type of object in an array of objects?

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related