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Object[] array = { 1, 2, new Object[]{ 3, 4, new Object[]{ 5 }, 6, 7 };

Integer[] flattenedArray = flatten(array);
//My function flatten(array) takes Object[]inputArray and returns it into flatten array of type
```
public static Integer[] flatten(Object[] inputArray) {
//function that does the operation and return Integer[]
}
```

What I have tried:

I have tried to collect it as stream and return as stream.toArray.
Stream<object> stream = Stream.of(inputArray);
stream= Arrays.stream(inputArray).flatMap(o->o instanceof Object[]? flatten((Object[])o): Stream.of(o));
Posted
Updated 18-Jul-23 3:01am

Yes, you can have an array of object type in Java. An array in Java is a container that holds a fixed number of values of a single type. The type of an array can be an object type, such as Object, or any other class type. For example, the following code creates an array of Object type that contains three elements: an int, a String, and another Object array:

JavaScript
Object[] array = { 1, "Hello", new Object[]{ 3, 4, 5 } };


To flatten this array using the Stream API, you can use the flatMap() method to convert each element in the array into a stream, and then concatenate all the streams into a single stream. You can then use the toArray() method to convert the stream of objects into an array of the desired type.

Here is an example of how you can implement the flatten() method to flatten an array of objects:

Java
<pre>public static Integer[] flatten(Object[] inputArray) {
    // Convert the input array into a stream of objects
    Stream<Object> stream = Arrays.stream(inputArray);

    // Recursively flatten the array by mapping each element to a stream
    // of objects, and then concatenating all the streams into a single stream
    stream = stream.flatMap(o -> o instanceof Object[] ? flatten((Object[])o) : Stream.of(o));

    // Convert the stream of objects into an array of integers
    Integer[] flattenedArray = stream.toArray(Integer[]::new);

    return flattenedArray;
}


You can then use the flatten() method as follows:

Object[] array = { 1, 2, new Object[]{ 3, 4, new Object[]{ 5 }, 6, 7 } };
Integer[] flattenedArray = flatten(array);


The resulting flattenedArray will be an array of integers containing the following elements: [1, 2, 3, 4, 5, 6, 7].
 
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Comments
Vibhanshu 2022 11-Dec-22 9:43am    
Using the code format I am having error when I am trying to call flatten recursively
stream = stream.flatMap(o -> o instanceof Object[] ? flatten((Object[])o) : Stream.of(o));

Since my function is expecting Integer[] as return type can that be the cause?

Error-> unhandled exception
CodeGuru84 11-Dec-22 11:43am    
It is possible that the error you are experiencing is due to the fact that the flatten function you are calling is returning a Stream<integer>, but the lambda expression in the flatMap method is expecting a Stream<object>.

If this is the case, you can fix the error by changing the return type of the flatten function to Stream<object> and casting the elements of the input array to Object before returning them in the stream:

private static Stream<object> flatten(Object[] arr) {
return Arrays.stream(arr).map(x -> (Object)x);
}

Alternatively, you can change the lambda expression in the flatMap method to expect a Stream<integer> by removing the typecast to Object:

stream = stream.flatMap(o -> o instanceof Integer[] ? flatten((Integer[])o) : Stream.of(o));
public static Object[] flatten(Object[] arr) {
		Stream<Object> stream = Arrays.stream(arr);
		
		stream = stream.flatMap(o -> o instanceof Object[] ? Stream.of(flatten((Object[]) o)) : Stream.of(o));
		
		Object[] flattenedArray = stream.toArray(Object[]::new);
		
		return flattenedArray;
		
	}
 
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