Java: NullPointerException 2D array of objects even array is initialized and filled

Question

In a method forest() I create a 2D array of objects then I fill it. I am sure that the array is filled because I can display the content of the array in class Forest in method forest() as well as in class Tree in method setTree() as shown below. Unfortunately, I can't get to this content by method showContentOfTree() or elsewhere. An error apears: NullPointerException

The question is why it happens and what I should change?

public class Forest extends JPanel {
    private LoadImage loadImage;
    private Tree[][] tree;

    public forest(){
        setLayout(null);
        loadImage = new LoadImage();
        loadImage.Image();
        Tree[][] tree = new Tree[16][16];
        for (int y = 0; y < 16; y++){
            for (int x = 0; x < 16; x++){
                tree[x][y] = new Tree();
                tree[x][y].setTree(loadImage.loadForest(x,y));
                System.out.println("Tree species " + tree[x][y].treeSpecies);
                //here System displays loaded treeSpecies successfully
            }
        }
        showContentOfTree();
    }
    public void showContentOfTree(){
    for (int y = 0; y < 16; y++){
        for (int x = 0; x < 16; x++){
            System.out.println("Tree species" + tree[x][y].treeSpecies);
                            //here System DOES NOT displays loaded treeSpecies:
                            //Error apears: java.lang.NullPointerException
                            //at Forest.showContentOfTree(Forest.java:31)
        }
    }
}

public class Tree{
    String treeSpecies;
    public void setTree(String treeSpecies){
        this.treeSpecies = treeSpecies;
        System.out.println("Tree species " + treeSpecies);
                //here System also displays loaded treeSpecies successfully
    }
}

Stack trace:

Exception in thread "main" java.lang.NullPointerException at Forest.showContentOfTree(Forest.java:31) 
at Forest.<init>(Forest.java:26) 
at Okno.<init>(Okno.java:19)

at Glowny.main(Glowny.java:10)

Answer 1

You are shadowing your tree variable in your forest method.

public forest(){
        setLayout(null);
        loadImage = new LoadImage();
        loadImage.Image();
        tree = new Tree[16][16]; //<-- remove Tree[][]