CodeGym/Help with Java Tasks/help please...what cause wrong output

Level 9

Mohali

26.09.2018
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help please...what cause wrong output

Question about the task

Cat relations

Java Syntax, Level 6, Lesson 11

Under discussion

wrong output

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); String grandMotherName = reader.readLine(); Cat catGrandMother = new Cat(grandMotherName); String fatherName = reader.readLine(); Cat catFather = new Cat(fatherName, catGrandFather); String motherName = reader.readLine(); Cat catMother = new Cat(motherName, catGrandMother); 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 , father , parent; Cat(String name) { this.name = name; } Cat(String name, Cat parent) { this.name = name; this.parent = parent; } Cat(String name, Cat mother, Cat father){ this.name = name; this.mother = mother; this.father = father; } @Override public String toString() { if (parent == null){ return "The cat's name is " + name + ", no mother, no father "; } else { if(father == null){ return "The cat's name is "+ name +", no mother, "+parent.name+" is the father"; } else if(mother == null){ return "The cat's name is "+ name +", "+parent.name+" is the mother, no father"; } else { return "Cat name is " + name + ", " + mother.name + " is the mother, " + father.name + ", is the father"; } } } } }

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Learner

Level 16 , India

27 September 2018, 06:16

1. Line 25: The statement calls your constructor Cat(String name, Cat parent) because there are only two arguments, so, it cannot call the other constructor with 3 arguments. 2. Now, in that Constructor, you are assigning value to Parent variable (not mother or father). Therefore, mother is null and Father is null. 3. Coming to toString() method which is called when you call print statement. Line 66: if Father is null, print the following statement. Refer point 2 above. Is Father null? Yes! Therefore, print the following statement: The cat's name is Mother Missy, no mother, Grandmother Puss is the father

Shahanshah Alam

Level 9 , Mohali, India

27 September 2018, 08:48

how can i resolve it?

Learner

Level 16 , India

27 September 2018, 08:58

Start by removing Parent attribute from the class. A parent is either a Father or a Mother. You can assign values directly to either a Father or a Mother attribute.

Shahanshah Alam

Level 9 , Mohali, India

27 September 2018, 09:08

then how constructor will determine which variable is being called?

Learner

Level 16 , India

27 September 2018, 09:20

Pass null for the object you don't want. So, if there is no Father, then pass name, mother, null.

Shahanshah Alam

Level 9 , Mohali, India

27 September 2018, 09:38

public String toString() { if (father == null && mother == null) return "The cat's name is " + name + ", no mother, no father "; else if(father == null || mother == null){ if(mother == null){ return "The cat's name is "+name+", no mother, "+father.name+" is the father"; }else { return "The cat's name is "+name+", "+mother.name+" is the mother, no father"; } }else{ return "The cat's name is "+name+", "+mother.name+" is the mother, "+father.name+" is the father"; } } } }

Shahanshah Alam

Level 9 , Mohali, India

27 September 2018, 09:39

i tried this all condition work properly except 4th one

Shahanshah Alam

Level 9 , Mohali, India

27 September 2018, 09:40

CONSTRUCTORS ARE:- Cat(String name) { this.name = name; } Cat(String name, Cat father) { this.name = name; this.father = father; } Cat(String name, Cat mother, Cat father){ this.name = name; this.mother = mother; this.father = father; }

Learner

Level 16 , India

27 September 2018, 09:41

How are you calling these constructors when creating the object? Cat catMother = new Cat(?);

Shahanshah Alam

Level 9 , Mohali, India

27 September 2018, 09:50

Cat catMother = new Cat(motherName, catGrandMother);

Learner

Level 16 , India

27 September 2018, 11:03

There was a lesson on this somewhere. I recommend you go back and read it carefully. This is how constructor works: You have defined 3 constructors: 1. Cat(String name) : Constructor with 1 argument of type String 2. Cat(String name, Cat father) : Constructor with 2 arguments of types String and Cat 3. Cat(String name, Cat father, Cat mother) : Constructor with 3 arguments of types String, Cat and Cat. The program is only concerned about type of arguments that you pass (String, Cat) and not the name of the argument (name, Father). So, if you replaced Constructor 2 with Cat(String name, Cat mother) or even Cat(String a, Cat b), it will mean the same thing. Now, when calling a constructor to create a class object like Cat mother = new Cat(name, grandMother); You mean to pass grandMother as a Mother attribute. However, your program picks Constructor 2 because it only matches the types of arguments (String, Cat). Inside Constructor 2 you assign value as this.father = father. Therefore, your grandMother value gets assigned to father instead of mother. Hope you understand this concept. Now for the solution part: As I stated before, if you were to pass the arguments like this Cat mother = new Cat(name, grandMother, null) The program will pick Constructor 3 because you are now passing three arguments which matches the definition of constructor 3. And, since, you are passing grandMother as the second argument in this case, it will be assigned to mother as defined in your Constructor 3.

Shahanshah Alam

Level 9 , Mohali, India

27 September 2018, 11:08

got it bro...thanks

Atif Saeed

Level 7 , Islamabad, Pakistan

29 September 2018, 07:40

this will not work for me

Atif Saeed

Level 7 , Islamabad, Pakistan

29 September 2018, 07:41

as the code is same with different variables name

Learner

Level 16 , India

1 October 2018, 04:52

Variable names do not affect the program logic.

Tayyab Mubeen

Level 16 , Lahore, Pakistan

3 October 2018, 17:26

how can i assign values am confused....can you please explain some logic

Learner

Level 16 , India

4 October 2018, 04:51

Assign values where? To class objects? Through constructor? I am not sure what you are asking. Please be specific.

Tayyab Mubeen

Level 16 , Lahore, Pakistan

4 October 2018, 09:52

assign values through constructor to String Cat and String Cat where once mother is null and once father is null

Learner

Level 16 , India

5 October 2018, 06:21

For Constructor: Cat(String name, Father f, Mother m) { this.name = name; this.father - f; this.mother = m; } If you call it and pass the following arguments: Cat("cat", f, null) then Father object will be f while Mother object will be null. It is same as directly setting any object to null. For example: Object obj = null; Similarly you can also call the constructor where father is null: Cat("a", null, m) or where both are null (although not required in this task): Cat("abc", null, null)