Clueless

Question about the task

This age doesn't work for me…

Java Syntax, Level 3, Lesson 4

Under discussion

Literally have no clue what's wrong here... Would love a good explanation. thanks upfront :)

Think about what the program is doing.
Fix the programming error so that person.age changes value.

Hint: carefully review the adjustAge method.

Requirements:

The program should display text on the screen.
The Person class should have a public int field called age.
The Person class's adjustAge method should display text on the screen.
The Person class's adjustAge method must have only one int parameter named age, and the method must be void.
The main method should call the adjustAge method only once.
The Person class's adjustAge method should increase the Person's age by 20.

package en.codegym.task.jdk13.task04.task0401; /* This age doesn't work for me… */ public class Solution { public static void main(String[] args) { Person person = new Person(); System.out.println("Age: " + person.age); person.adjustAge(person.age); System.out.println("Adjusted age: " + person.age); } public static class Person { public int age = 20; public void adjustAge(int age) { age = age + 20; System.out.println("The age in adjustAge() is: " + age); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

30 October 2024, 14:01

Program flow will go line by line with a few structures that redirect flow. Examples of structures that redirect program flow are conditional statements (loops, if statements, etc), methods, constructors, and a few other things (keeping this example light as you will learn about this later). So, here is how this code flows: Line 8: All Java programs start with a main() method. In this code the main method starts on line 8, so this is where there code starts. Line 9: This line is ab Object creation line, specifically a Person object. This is done correctly by first declaring the type of object (Person), naming the variable that will store this object (person), then by using the assingment operator (equals '='), setting that variable to the value of a new object using new Person(). Program flow is interrupted here as the code new Person() calls a constructor in the Person class. Line 15: The Person class does not have a constructor in it so Java calls one internally that we refer to as the default constructor. This ONLY occurs when there are no other constructors present. The default constructor does not have any code it runs as its only purpose is to satisfy a rule that Java requires a constructor in each and every class. I won't go into why you would want to create your own constructors and not just simply use the default constructor; you will learn this later. Line 16: When an new object is created any variables inside the class will be initialized. This line says that the age variable in the Person class is set initially to 20. Line 9: The program was interrupted at line 9 to create a Person object. When the person object is finished being created the program flow to where it was interrupted.

Guadalupe Gagnon

Level 37 , Tampa, United States

30 October 2024, 14:19

Line 10: This outputs ("Age: " + person.age). The program first needs to find where person.age is. It does this by first pulling up the object connected to the variable 'person', then it calls the variable 'age' stored in that object. It can then create the String necessary to pass to the System.out.println() method. Calling methods interrupts program flow and does so in this case; however I won't go into this and you really don't need to know more than the basics unless you become a master at Java who contributes to its code base. The result is the String is output. In this case you get "Age: 20". Line 11: This line uses the variable 'person' to call the method adjustAge(). This method is declared on line 18 and it requires an int to be passed in. You can tell by looking at the method declaration and seeing what is in the parentheses (int age). So, back on line 11, inside the parentheses the code passes in person.age, which is an int. We know from before that person.age has the program get the age variable from the person class, which is 20. Because this is a method program flow is interrupted and will go to the method. The value in parentheses is carried along to the next step. Line 18: The method has been called. First thing is that any values that are needed by the method are set. These are called the method parameters and reside inside the parentheses on the method line. When you call a method you MUST pass in values to the method that match these parameters. This method requires an int, and in the previous step I explained an int value 20 was passed in. The int parameter variable is named 'age' which is where the value 20 is stored and can be used in the method. It is the same thing as if the first line of the method was:

int age = 20;

Line 19: This line, using the assignment operator, sets the variable age to age + 20.

Guadalupe Gagnon

Level 37 , Tampa, United States

30 October 2024, 14:27

Line 20: this is another output line, i'll skip a deep explanation but it outputs "The age in adjustAge() is: 40". This is the last line of the method so program flow is going to go back to where the method was called, which is line 11. Line 11: the flow returns here Line 12: This line does the same thing as line 10 and outputs the text. The line should output a different 'age' than line 10, but the output ("Adjusted age: 20") indicates that age has not changed after the method was called on line 11 even though the output from line 20 says that it was changed to 40. So the method on line 18 should change the 'age' on line 16 and the task is asking you to fix whatever bugs are present that prevent this from happening.

LeonThePro

Level 4 , Israel

30 October 2024, 17:27

First of all thanks for the very detailed explanation! It still seems a bit chinses to me in any case.. My question what is a constructor and when did the course speak about it?

Guadalupe Gagnon

Level 37 , Tampa, United States

30 October 2024, 20:33

Constructors are a necessary part of Object Orientated Programming that are called every time an object is created. The 'new' keyword is used in Object creation, so when you see that then a Constructor is being called. I tried to keep my explanation in the above posts short but its hard for me to remember exactly how it was when I was at level 3 and there are some terms and references that are above level 3. I wouldn't worry too much about them at this point as they will all be explained at later points in the course, with practice in using them.