Question

How do I initialise a heap data structure in simple, basic Java pseudo-code with 7 numbers?

Answer 1

If you want to do it yourself and not use Java’s PriorityQueue then you have to put all X items at the right place so they uphold heap properties:

//This will switch the current item with it's greatest child, if this child is
//larger than the current item itself.
private void percolateDown(int i){
    //Get n's greatest child. The two children are at position 2i+1 and 2i+2
    int n = getGreatestChild(i);

    //Don't do anything if the greater child is smaller or equal to the parent
    if( yourNumbersArray[n] <= yourNumbersArray[i] )
        return;

    //Now switch the parent with the greatest child

    //Make sure that the newly placed item is at the right spot by percolating it again.
    percolateDown(n);
}

private void initialize(){
    //Call the percolateDown() function for all items of your array.
    //Due to the heap nature you can leave out the second half, though. 
    int mid = yourNumbersArray.length/2;

//Start in the middle and work your way towards the front.
//This way you'll first sort the lowest level of your heap, then the second lowest, and so on.
    for(; mid>=0; --mid){
        percolateDown(mid);
    }
}

When looking for the greatest child of any item you have to remember that one or both children could be outside of your array. In this case you don’t have to take it into account, of course.