I want to write to a variable only if there isn't anything already there. Here is my code so far.
if (inv[0] == null) {
inv[0]=map.getTileId(tileX-1, tileY-1, 0);
}
It gives me this error:
java.lang.Error: Unresolved compilation problem:
The operator == is undefined for the argument type(s) int, null
inv is an int[]
, and int
cannot be null
, since it is a primitive and not a reference.
int
s are initialized to zero in java.
I'm assuming inv
is an int[]
.
There's no such concept as a value "existing" or not in an array. For example:
int[] x = new int[5];
has exactly the same contents as:
int[] x = new int[5];
x[3] = 0;
Now if you used an Integer[]
you could use a null value to indicate "unpopulated"... is that what you want?
Arrays are always filled with the default value for the element type to start with - which is null
in the case of reference types such as Integer
.
I take it that inv
is an int[]
. You can't compare an int
to null
, null
only applies to reference types, not primitives. You have to either assign it some kind of flag value instead ( 0
being popular, and the value it will have by default when you create the array), or make inv
an Integer[]
instead ( Integer
being a reference type, it is null
-able).
I'm assuming from error message, that inv[]
is array of int
, and int
in java is not an object, so it cannot have null
value.. You have to compare it with 0
(default value on each index of empty int array)..
A primitive can not be null in Java.
Well... int
is a primitive type. That can't be null.
You can check the size of the array:
int[] arr = new int[10]; System.out.println( arr.size() );
The plain arrays are indexed from 0 to their size - 1, and no value can be missing. So in your code, you are asking whether the first member of type int
is null
, which can't happen - either it's a number or it will cause ArrayOutOfBoundsException
.
If you want to have a "sparse array" similar to what PHP or JavaScript, you need a Map
:
Map<Integer, Integer> map = new HashMap();
map.put( 1, 324 );
if( map.get( 2 ) == null ) ...
You could try something like this
Integer[] inv = new Integer[10];
inv[0] = 1;
inv[1] = 2;
....
if(inv[3] == null)
{
inv[3] = getSomeValue();
}
The error is because inv
is an array of int
, not the object wrapper Integer
. Your array comes initialized for you anyway. If you wrote
int[] inv = new int[5];
you will have an array of 5 zeroes.
You should initialize your array yourself using some value that you know is invalid (eg if you had an array of ages, a negative value would be invalid). Check for the invalid value and if it's there, replace it.
primitive types can't be compared to null.
You can test if the number if > 0 to see if a value exists:
if(inv[0] <= 0)
{
inv[0]=map.getTileId(tileX-1, tileY-1, 0);
}
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