CodeGym/Help with Java Tasks/Bonvolu helpu min - please help me

Level 15

Toeroekbalint

01.04.2019
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8comments

Bonvolu helpu min - please help me

Question about the task

Static modifiers are out of place

Java Syntax, Level 9, Lesson 11

Resolved

EO - Mi provas cxion, sed sistemo ne akceptas. EN - I try everything, but system does not accept it.

package com.codegym.task.task09.task0925; /* Static modifiers are out of place */ public class Solution { public int A = 5; public int B = 2 * A; public int C = A * B; static int D; static int E = Solution.D; // public int D = A * B; public static void main(String[] args) { Solution room = new Solution(); room.A = 5; Solution.D = 5; } public int getA() { return A; } }

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Satya Vath

Level 31 , Vijayawada, India

6 April 2019, 12:46

package com.codegym.task.task09.task0925;

/*
Static modifiers are out of place

*/

public class Solution {
    public static int A = 5;
    public static int B = 2 * A;
    public int C = A * B;
    public static int D = A * B;

    public static void main(String[] args) {
        Solution room = new Solution();
        room.A = 5;

        Solution.D = 5;
    }

    public int getA() {
        return A;
    }

}

Guadalupe Gagnon

Level 37 , Tampa, United States

1 April 2019, 20:09

Are you using intelliJ? Reset the task and look for the errors, they will solve this for you. You literally have to add three words to the existing code to solve this. Now if you want to know how to solve this other than "intelliJ solved it for me": Take for example this bit of code:

Class Dog{
   int age;
   static int Age;
}

in calling code you would have to set the non static variable age variable like this:

Dog rex = new Dog(), spike = new Dog();
rex.age = 4;
spike.age = 3;

For the static variable 'Age', you do not need to create an object and can just use code to set like this:

Dog.Age = 7;

For testing you could add code like the following to see how it works:

System.out.println("rex.age = " + rex.age + " -- rex.Age = " + rex.Age );
System.out.println("spike.age = " + spike.age + " -- spike.Age= " + spike.Age );

Notice in the above code i used an object to reference both 'age' and 'Age', this is legit though you can access the static variable with Dog.Age (like done with setting it above). The above code would output: rex.age = 4 -- rex.Age = 7 spike.age = 3 -- spike.Age = 7 Now just change rex.Age (the static variable) and you will see it reflected on both objects when output:

rex.Age = 10;
System.out.println("rex.age = " + rex.age + " -- rex.Age = " + rex.Age );
System.out.println("spike.age = " + spike.age + " -- spike.Age= " + spike.Age );

The above code would output: rex.age = 4 -- rex.Age = 10 spike.age = 3 -- spike.Age = 10

Guadalupe Gagnon

Level 37 , Tampa, United States

1 April 2019, 20:11

Now going back to the task, line 21 is calling the variable 'D' without creating an object, which means that 'D' has to be static for this code to work. Static variables remain the same for every single object that is created, so code like 'public int D = A * B;' would only be valid if both 'A' and 'B' are static as well, because if they were not static then they could hold different values for each different object created and thus 'D' would not be the same over every single object. So the quick rules explained above: Static Varaibles: - do not need an object to be referenced - have the same value for every single (same) object created - if other class variables (properties) are used to set its value, those variables MUST be static Non-Static Varaibles - can only be referenced with a created object - can have static and non static class variables to set value - can hold different values for each new object created

Kisszol

Level 15 , Toeroekbalint, Hungary

2 April 2019, 06:47

solution

dankon. mia problemo estis ke mi ne donis la public antaux la static. thanks my problem was that I did not add the publi before the static. jen mia solvo: public class Solution { public static int A = 5; public static int B = 2 * A; public int C = A * B; public static int D = A * B; // static int E = Solution.D; // public int D = A * B; public static void main(String[] args) { Solution room = new Solution(); room.A = 5; Solution.D = 5; } public int getA() { return A; } }

Guadalupe Gagnon

Level 37 , Tampa, United States

2 April 2019, 13:15

solution

Glad you figured it out. Resetting the task would have helped there because the starting code had the 'public' modifier.You must have removed it by accident between testing out possible solutions for the problem.

TXH

Level 18 , London, United Kingdom

20 August 2019, 14:54

thank you so much for telling us:)

The Chief

Level 18 , United States

15 April 2021, 22:01

G, the objects created in both this task and your post are of the same name (Solution, Dog) as the class. The reason for that is because the class is the blueprint from which individual objects are created. Is that correct?

Guadalupe Gagnon

Level 37 , Tampa, United States

16 April 2021, 01:14

Exactly. It is often described as a blueprint, which is a simple approach to it, but easy to understand when you are first learning. The slightly more complicated, but also more accurate, answer is that a class is a definition of state and behavior. The actual class itself doesn't do anything, but each object of that class has all the fields and methods defined in the class. Fields are what describe the state and methods describe the behavior of objects. So the simple Dog class I made above has a field called "age" which would be the state of any dog object created. That all may be a bit complicated for you now, but you have been successfully using the behavior of many objects up to this point. Take the BufferedReader class, you should be familiar with it; and if not that then the Scanner class; they both have the behavior that they read input (user input, file input, even network input). You get the desired behavior by calling the appropriate methods. The state of the object is first initialized with the constructor and involves you passing the desired input stream to the object. All objects behave in similar fashion... initialized to starting state, use methods to get behavior; some method behavior is to change state, such as adding and removing items from an ArrayList. Anyways, all these classes have class code hidden back in the JDK. You can actually look it up in intelliJ.... but I wouldn't recommend spending too much time on it because the code is very complicated. That is actually a key aspect of Object Orientated Programming: taking complicated code and hiding it behind simple interfaces (behavior).