create a Map from int array with index as key and value as array element in java

Question

this is a integer array I have

[9,3,15,20,7]

I want to create a map like

0->9 1->3

with index as key and array element as value

IntStream.range(0,postorder.length).collect(Collectors.toMap(i -> postorder[i],i->i));

I tried like this but getting compilation error as required type int found object is there any to create map like this using streams in java

Aditya Rewari · Accepted Answer · 2021-07-17 07:08:00Z

2

You should have boxed() the IntStream

final int[] postorder = {2,5, 6, 8};
Map<Object, Object> map = IntStream
        .range(0,postorder.length)
        .boxed()
        .collect(Collectors.toMap(index -> index, index-> postorder[index]));
System.out.println(map);

edited Jul 17, 2021 at 7:08

answered Jul 17, 2021 at 7:02

Aditya Rewari

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ZIHAO LIU · Accepted Answer · 2021-07-17 06:55:35Z

1

IntStream.range(0, postorder.length)
         .boxed()
         .collect(Collectors.toMap(i -> i, i -> postorder[i], (a, b) -> b));

answered Jul 17, 2021 at 6:55

ZIHAO LIU

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2 Comments

user3878073 Over a year ago

this worked can you explain about this I can't understand the (a, b) -> b) part

ZIHAO LIU Over a year ago

In your case, you can remove (a, b) -> b part, .collect(Collectors.toMap(i -> i, i -> postorder[i]); will works as well. (a, b) -> b) is a merge function, it will be used if there is duplicate key of map. In your case it can be ignored. You can see the api doc docs.oracle.com/javase/8/docs/api/java/util/stream/…

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