NullPointerException in line 67

Question about the task

Under discussion

Hi, I don't understand why I get a null pointer exception in line 67, and what's wrong with my code? Can someone help me, thank you :-)

1. Create a Human class with String name, boolean sex, int age, and ArrayList<Human> children fields.
2. Create and populate objects so that we end up with: two grandfathers, two grandmothers, one father, one mother, and three children.
3. Display all the Human objects (Hint: use the Human class's toString() method).

Requirements:

The program should display text on the screen.
The Human class must have four fields.
The Human class must have one method.
The Solution class must have one method.
The program should create objects and fill them with data to get two grandfathers, two grandmothers, one father, one mother, and three children. Then it should display all the Human objects on the screen.

package com.codegym.task.task08.task0824; import java.util.ArrayList; /* Make a family */ public class Solution { public static void main(String[] args) { ArrayList<Human> children = new ArrayList<>(); Human child1 = new Human("Anita", false, 30); children.add(child1); Human child2 = new Human("Allan", true, 27); children.add(child2); Human child3 = new Human("Katrine", false, 24); children.add(child3); Human grandfather1 = new Human("Jens", true, 90); Human grandfather2 = new Human("Børge", true, 86); Human grandmother1 = new Human("Else", false, 90); Human grandmother2 = new Human("Olfa", false, 90); Human father1 = new Human("Henrik", true, 52, children); Human mother1 = new Human("Signe", false, 60, children); System.out.println(grandfather1.toString()); System.out.println(grandfather2.toString()); System.out.println(grandmother1.toString()); System.out.println(grandmother2.toString()); System.out.println(father1.toString()); System.out.println(mother1.toString()); for (Human child : children) { System.out.println(child); } } public static class Human { String name; boolean sex; int age; ArrayList<Human> children; public Human(String name, boolean sex, int age) { this.name = name; this.sex = sex; this.age = age; } public Human(String name, boolean sex, int age, ArrayList<Human> children) { this.name = name; this.sex = sex; this.age = age; this.children = children; } public String toString() { String text = ""; text += "Name: " + this.name; text += ", sex: " + (this.sex ? "male" : "female"); text += ", age: " + this.age; int childCount = this.children.size(); if (childCount > 0) { text += ", children: " + this.children.get(0).name; for (int i = 1; i < childCount; i++) { Human child = this.children.get(i); text += ", " + child.name; } } return text; } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

28 December 2020, 16:15

The children list at line 46 is null when you create a new Human object that uses the constructor at line 48. This means the objects at line 14, 17, 20, 23, 24, 25, and 26 all have null "children" lists. For each of these, when the .toString() method is called line 67 gets a null pointer exception thrown when trying to call the .size() method of the List class. Also, the println() method calls toString() on any and all objects passed to it. You do not need to do that:

// these two lines are exactly the same,
// but the second one is cleaner and less typing
System.out.println(grandfather1.toString());
System.out.println(grandfather1);