Can Java use a String as an index array key? Example:
array["a"] = 1;
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3what about multidimensional array like array["a"]["b"]?Vikas Kumar– Vikas Kumar2014-01-16 01:43:52 +00:00Commented Jan 16, 2014 at 1:43
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4 Answers
No.
To do something like this, you have to use a Map.
Map<String, Integer> aMap = new HashMap<String, Integer>();
aMap.put("a" , Integer.valueOf(1));
2 Comments
mre
+1, But couldn't you use
Integer.valueOf(1) since a new Integer instance isn't really required? Actually, you could just use the constant 1 instead of needlessly wrapping, right?
Michael Berry
@mre the only advantage with not using the constant is that it'll work with versions before 1.5 when autoboxing was introduced. For all modern versions though I agree the constant would be better!
No - you want a map to do that:
Map<String, Integer> map = new HashMap<>();
map.put("a", 2);
Then to get it:
int val = map.get("a"); //2
You can only use the square bracket syntax for arrays, not for any of the collections. So something like:
int val = map["a"]; //Compile error
Will always be illegal. You have to use the get() method.
Comments
No, that would be a Map in Java.
(The type would be Map<String,Integer>.)
Comments
No they can't. But they can use chars the ASCII value of the alphabet will be used as the key index
Consider
String[] a = new String['a' + 1];
a['a'] = "Hello";
int[] b = new int['a' + 3];
b['c'] = 5;
System.out.println(a[97]);
System.out.print(b[99]);
This will output
Hello
5
10 Comments
cyroxis
Your arrays is of size 98 to store two values, also 99 (for 'c') is out of range.
goonerify
The arrays are indeed large for something so simple, however, the question is about whether Java can use a String as an index array key not about how efficient it is. Also, the ascii code for 'a' is 97, add 3 to that and you arrive at 100 for the size of array b. Since the ascii code for 'c' is 99, you can access the value at the 99th index of the array without throwing any
IndexOutOfBoundsExceptions. If you have no more reservations, please undo your downvote, so that this answer can be useful to other readers, even if just from a purely educational standpointgoonerify
Such operations are actually used in algorithms like R-way Tries where the Radix is the total number of ASCII characters available, so it's not entirely uncommon or inefficient to work with arrays this way
tony gil
while a workaround is technically a solution, this one is a really, really, really bad suggestion in 9,999 cases out of 10,000. i recommend that you post a serious disclaimer or you will keep on being downvoted. note: i personally did NOT downvote you. but i came THIS close.
NurShomik
Just wanted to point out: the OP wanted to know if arrays can have a String as index, not a character.
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