Quick Union Algorithm Java Implentation

Quick Union Algorithm

public class quickUnion {
	private int[] id;
	
	public void QuickUnionUF(int N){
		id = new int [N];
		for(int i = 0; i < N; i++){
			id[i] = i;
		}
	}
	
	private int root(int i){
		while (i != id[i]){
			i = id[i];
		}
		return i;
	}
	public boolean connected(int p, int q){
		return root(p) == root(q);
	}
	public void union(int p, int q){
		int i = root(p);
		int j = root(q);
		id[i] = j;
	}
}

I don't understand why the root function couldn't just be

private int root(int i){ return id[i]; }

Each union changes the root of the element to the root so wouldn't that make id[i] always the root? And it it doesn't why would i=id[i]; work, satisfying the while loop?

I don't understand why the root function couldn't just be

private int root(int i){ return id[i]; }

Each union changes the root of the element to the root so wouldn't that make id[i] always the root? And it it doesn't why would i=id[i]; work, satisfying the while loop?

The i = id[i] is represent the moving check from its current node to its parent node, it will loop until i == id[i] which by default the number is the parent of itself.