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Why is this int array not passed as an object vararg array?

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12

I used this code. I am confused why this int array is not converted to an object vararg argument:

class MyClass 
 static void print(Object... obj) 
 System.out.println("Object…: " + obj[0]);
 

 public static void main(String[] args) 
 int[] array = new int[] 9, 1, 1;
 print(array);
 System.out.println(array instanceof Object);
 

I expected the output:

Object…: 9
true

but it gives:

Object…: [I@140e19d
true

java

share|improve this question

edited May 11 at 20:39

Boann

37.8k1291123

asked May 11 at 17:37

JoeCrayonJoeCrayon

774

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  The issue is that Object... means Object[] and int[] can not be converted to Object[] (int is a primitive, not an Object). However, the int[] array itself can be interpreted as Object. So you end up passing an object array Object[] with exactly one element in it, an int[]. So you have an array of arrays.
  
  – Zabuza
  May 11 at 18:27
  
  

  
  
  
  

add a comment | 

12

I used this code. I am confused why this int array is not converted to an object vararg argument:

class MyClass 
 static void print(Object... obj) 
 System.out.println("Object…: " + obj[0]);
 

 public static void main(String[] args) 
 int[] array = new int[] 9, 1, 1;
 print(array);
 System.out.println(array instanceof Object);
 

I expected the output:

Object…: 9
true

but it gives:

Object…: [I@140e19d
true

java

share|improve this question

edited May 11 at 20:39

Boann

37.8k1291123

asked May 11 at 17:37

JoeCrayonJoeCrayon

774

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  The issue is that Object... means Object[] and int[] can not be converted to Object[] (int is a primitive, not an Object). However, the int[] array itself can be interpreted as Object. So you end up passing an object array Object[] with exactly one element in it, an int[]. So you have an array of arrays.
  
  – Zabuza
  May 11 at 18:27
  
  

  
  
  
  

add a comment | 

I used this code. I am confused why this int array is not converted to an object vararg argument:

class MyClass 
 static void print(Object... obj) 
 System.out.println("Object…: " + obj[0]);
 

 public static void main(String[] args) 
 int[] array = new int[] 9, 1, 1;
 print(array);
 System.out.println(array instanceof Object);
 

I expected the output:

Object…: 9
true

but it gives:

Object…: [I@140e19d
true

java

share|improve this question

edited May 11 at 20:39

Boann

37.8k1291123

asked May 11 at 17:37

JoeCrayonJoeCrayon

774

class MyClass 
 static void print(Object... obj) 
 System.out.println("Object…: " + obj[0]);
 

 public static void main(String[] args) 
 int[] array = new int[] 9, 1, 1;
 print(array);
 System.out.println(array instanceof Object);
 

Object…: 9
true

Object…: [I@140e19d
true

share|improve this question

edited May 11 at 20:39

Boann

37.8k1291123

asked May 11 at 17:37

JoeCrayonJoeCrayon

774

share|improve this question

edited May 11 at 20:39

Boann

37.8k1291123

asked May 11 at 17:37

JoeCrayonJoeCrayon

774

edited May 11 at 20:39

Boann

37.8k1291123

edited May 11 at 20:39

Boann

37.8k1291123

asked May 11 at 17:37

JoeCrayonJoeCrayon

774

asked May 11 at 17:37

JoeCrayonJoeCrayon

774

3 Answers
3

active

oldest

votes

21

You're running into an edge case where objects and primitives don't work as expected.
The problem is that the actual code ends up expecting static void print(Object[]), but int[] cannot be cast to Object[]. However it can be cast to Object, resulting in the following executed code: print(new int[][]array).

You get the behavior you expect by using an object-based array like Integer[] instead of int[].

share|improve this answer

answered May 11 at 17:42

KiskaeKiskae

14.3k13244

add a comment | 

8

The reason for this is that an int array cannot be casted to an Object array implicitly. So you actually end up passing the int array as the first element of the Object array.

You could get the expected output without changing your main method and without changing the parameters if you do it like this:

static void print(Object... obj) 
 System.out.println("Object…: " + ((int[]) obj[0])[0]);

Output:

Object…: 9
true

share|improve this answer

edited May 11 at 18:30

answered May 11 at 17:39

ruoholaruohola

3,4142635

add a comment | 

0

As you know, when we use varargs, we can pass one or more arguments separating by comma. In fact it is a simplification of array and the Java compiler considers it as an array of specified type.

Oracle documentation told us that an array of objects or primitives is an object too:

In the Java programming language, arrays are objects (§4.3.1), are
dynamically created, and may be assigned to variables of type Object
(§4.3.2). All methods of class Object may be invoked on an array.

So when you pass an int[] to the print(Object... obj) method, you are passing an object as the first element of varargs, then System.out.println("Object…: " + obj[0]); prints its reference address (default toString() method of an object).

share|improve this answer

answered May 12 at 4:59

aminographyaminography

6,91522136

add a comment | 

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21

You're running into an edge case where objects and primitives don't work as expected.
The problem is that the actual code ends up expecting static void print(Object[]), but int[] cannot be cast to Object[]. However it can be cast to Object, resulting in the following executed code: print(new int[][]array).

You get the behavior you expect by using an object-based array like Integer[] instead of int[].

share|improve this answer

answered May 11 at 17:42

KiskaeKiskae

14.3k13244

add a comment | 

21

You're running into an edge case where objects and primitives don't work as expected.
The problem is that the actual code ends up expecting static void print(Object[]), but int[] cannot be cast to Object[]. However it can be cast to Object, resulting in the following executed code: print(new int[][]array).

You get the behavior you expect by using an object-based array like Integer[] instead of int[].

share|improve this answer

answered May 11 at 17:42

KiskaeKiskae

14.3k13244

add a comment | 

You're running into an edge case where objects and primitives don't work as expected.
The problem is that the actual code ends up expecting static void print(Object[]), but int[] cannot be cast to Object[]. However it can be cast to Object, resulting in the following executed code: print(new int[][]array).

You get the behavior you expect by using an object-based array like Integer[] instead of int[].

share|improve this answer

answered May 11 at 17:42

KiskaeKiskae

14.3k13244

share|improve this answer

answered May 11 at 17:42

KiskaeKiskae

14.3k13244

answered May 11 at 17:42

KiskaeKiskae

14.3k13244

answered May 11 at 17:42

KiskaeKiskae

14.3k13244

8

The reason for this is that an int array cannot be casted to an Object array implicitly. So you actually end up passing the int array as the first element of the Object array.

You could get the expected output without changing your main method and without changing the parameters if you do it like this:

static void print(Object... obj) 
 System.out.println("Object…: " + ((int[]) obj[0])[0]);

Output:

Object…: 9
true

share|improve this answer

edited May 11 at 18:30

answered May 11 at 17:39

ruoholaruohola

3,4142635

add a comment | 

8

The reason for this is that an int array cannot be casted to an Object array implicitly. So you actually end up passing the int array as the first element of the Object array.

You could get the expected output without changing your main method and without changing the parameters if you do it like this:

static void print(Object... obj) 
 System.out.println("Object…: " + ((int[]) obj[0])[0]);

Output:

Object…: 9
true

share|improve this answer

edited May 11 at 18:30

answered May 11 at 17:39

ruoholaruohola

3,4142635

add a comment | 

The reason for this is that an int array cannot be casted to an Object array implicitly. So you actually end up passing the int array as the first element of the Object array.

You could get the expected output without changing your main method and without changing the parameters if you do it like this:

static void print(Object... obj) 
 System.out.println("Object…: " + ((int[]) obj[0])[0]);

Output:

Object…: 9
true

share|improve this answer

edited May 11 at 18:30

answered May 11 at 17:39

ruoholaruohola

3,4142635

static void print(Object... obj) 
 System.out.println("Object…: " + ((int[]) obj[0])[0]);

share|improve this answer

edited May 11 at 18:30

answered May 11 at 17:39

ruoholaruohola

3,4142635

answered May 11 at 17:39

ruoholaruohola

3,4142635

answered May 11 at 17:39

ruoholaruohola

3,4142635

0

As you know, when we use varargs, we can pass one or more arguments separating by comma. In fact it is a simplification of array and the Java compiler considers it as an array of specified type.

Oracle documentation told us that an array of objects or primitives is an object too:

In the Java programming language, arrays are objects (§4.3.1), are
dynamically created, and may be assigned to variables of type Object
(§4.3.2). All methods of class Object may be invoked on an array.

So when you pass an int[] to the print(Object... obj) method, you are passing an object as the first element of varargs, then System.out.println("Object…: " + obj[0]); prints its reference address (default toString() method of an object).

share|improve this answer

answered May 12 at 4:59

aminographyaminography

6,91522136

add a comment | 

0

As you know, when we use varargs, we can pass one or more arguments separating by comma. In fact it is a simplification of array and the Java compiler considers it as an array of specified type.

Oracle documentation told us that an array of objects or primitives is an object too:

In the Java programming language, arrays are objects (§4.3.1), are
dynamically created, and may be assigned to variables of type Object
(§4.3.2). All methods of class Object may be invoked on an array.

So when you pass an int[] to the print(Object... obj) method, you are passing an object as the first element of varargs, then System.out.println("Object…: " + obj[0]); prints its reference address (default toString() method of an object).

share|improve this answer

answered May 12 at 4:59

aminographyaminography

6,91522136

add a comment | 

As you know, when we use varargs, we can pass one or more arguments separating by comma. In fact it is a simplification of array and the Java compiler considers it as an array of specified type.

Oracle documentation told us that an array of objects or primitives is an object too:

In the Java programming language, arrays are objects (§4.3.1), are
dynamically created, and may be assigned to variables of type Object
(§4.3.2). All methods of class Object may be invoked on an array.

So when you pass an int[] to the print(Object... obj) method, you are passing an object as the first element of varargs, then System.out.println("Object…: " + obj[0]); prints its reference address (default toString() method of an object).

share|improve this answer

answered May 12 at 4:59

aminographyaminography

6,91522136

share|improve this answer

answered May 12 at 4:59

aminographyaminography

6,91522136

answered May 12 at 4:59

aminographyaminography

6,91522136

answered May 12 at 4:59

aminographyaminography

6,91522136