// JAVA implementation of tree using array 
// numbering starting from 0 to n-1. 
import java.util.*;
import java.lang.*;
import java.io.*;

class bTree {
    public static void main(String[] args) {
        btree_Array obj = new btree_Array();
        obj.Root("P");
        // obj.set_Left("Q", 0); 
        obj.set_Right("R", 0);
        obj.set_Left("S", 1);
        obj.set_Right("T", 1);
        obj.set_Left("U", 2);
        obj.print_Tree();
    }
}

class btree_Array {
    static int root = 0;
    static String[] s = new String[10];

    /*create root*/
    public void Root(String key) {
        s[0] = key;
    }

    /*create left son of root*/
    public void set_Left(String key, int root) {
        int t = (root * 2) + 1;

        if (s[root] == null) {
            System.out.printf("Can't set child at %d, no parent found\n", t);
        } else {
            s[t] = key;
        }
    }

    /*create right son of root*/
    public void set_Right(String key, int root) {
        int t = (root * 2) + 2;

        if (s[root] == null) {
            System.out.printf("Can't set child at %d, no parent found\n", t);
        } else {
            s[t] = key;
        }
    }

    public void print_Tree() {
        for (int i = 0; i < 10; i++) {
            if (s[i] != null)
                System.out.print(s[i]);
            else
                System.out.print("-");

        }
    }
}

Can't set child at 3, no parent found
Can't set child at 4, no parent found
P-R--U----