Help I cannot resolve this

Question about the task

Cat relations

Java Syntax, Level 6, Lesson 11

Under discussion

All but the first two conditions have not been met, what could be the problem?

Task: Each cat has a name and a mother.
Create a class that describes this situation.
Create two objects: a daughter cat and a mother.
Display them on the screen.

New task: Each cat has a name, a father, and a mother.
Edit Cat so that it reflects these relationships.
Create 6 objects: grandfather (the father's father), grandmother (the mother's mother), father, mother, son, daughter.
Display them all in the following order: grandfather, grandmother, father, mother, son, daughter.

Example input:
Grandfather Tiger Grandmother Puss Father Oscar Mother Missy Son Simba Daughter Coco

Example output:
The cat's name is Grandfather Tiger, no mother, no father The cat's name is Grandmother Puss, no mother, no father The cat's name is Father Oscar, no mother, Grandfather Tiger is the father The cat's name is Mother Missy, Grandmother Puss is the mother, no father The cat's name is Son Simba, Mother Missy is the mother, Father Oscar is the father The cat's name is Daughter Coco, Mother Missy is the mother, Father Oscar is the father

Requirements:

The program should read in the names of 6 cats in the specified order.
The main method should create 6 Cat objects.
The program should display 6 lines with information about the cats.
The line about the grandfather (first line) must match the conditions.
The line about the grandmother (second line) must match the conditions.
The line about the father (third line) must match the conditions.
The line about the mother (fourth line) must match the conditions.
The line about the son (fifth line) must match the conditions.
The line about the daughter (sixth line) must match the conditions.

package com.codegym.task.task06.task0621; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /* Cat relations */ public class Solution { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String grandFatherName = reader.readLine(); Cat catGrandFather = new Cat(grandFatherName, null, null); String grandMotherName = reader.readLine(); Cat catGrandMother = new Cat(grandMotherName, null, null); String fatherName = reader.readLine(); Cat catFather = new Cat(fatherName, null, catGrandFather); String motherName = reader.readLine(); Cat catMother = new Cat(motherName, catGrandMother, null); String sonName = reader.readLine(); Cat catSon = new Cat(sonName, catMother, catFather); String daughterName = reader.readLine(); Cat catDaughter = new Cat(daughterName, catMother, catFather); System.out.println(catGrandFather); System.out.println(catGrandMother); System.out.println(catFather); System.out.println(catMother); System.out.println(catSon); System.out.println(catDaughter); } public static class Cat { private String name; private Cat mother; private Cat father; /* Cat(String name) { this.name = name; }*/ Cat(String name, Cat mother, Cat father) { this.name = name; this.mother = mother; this.father = father; } @Override public String toString() { if (mother == null) return "The cat's name is " + name + ", no mother, " + father.name + " is the father"; else if (father == null) return "The cat's name is " + name + ", " + mother.name + " is the mother" + ", no father"; else if (mother == null && father == null) return "The cat's name is " + name + ", no mother, " + " no father"; else return "The cat's name is " + name + ", " + mother.name + " is the mother" + ", " + father.name + " is the father"; } } }

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Dmitriy Bursa

Level 27 , Kyiv, Ukraine

13 July 2019, 15:58

line 34 when you call first time println with object, you are trying to get father's name, but object father is null (lines 60 and 61)

Cat catGrandFather = new Cat(grandFatherName, null, null);

try first check both parents

if (mother == null && father == null)

and after other

Nnaemeka

Level 8 , Lagos, Nigeria

13 July 2019, 18:52

Wow. Thank you! This solved the problem. But i'm not sure i fully understand why. Could you help explain better?

Dmitriy Bursa

Level 27 , Kyiv, Ukraine

13 July 2019, 19:31

will try to :) look, when you call first time println, program use toString method for output text. in your overrided method you check first

if (mother == null)

and return string. in your first call you use object Cat, who not have parent, but in first check this object you try to get name of nonexistent father. Program check mother, it's null, and exiting with exception NullPointerException, becouse father also not exist, but you try get his name. That's why first you must check both parents