Return type Error

Question about the task

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I'm getting this error "invalid method declaration; return type required. file com/codegym/task/task14/task1418/Solution.java, line 26, position 608" I didn't think the last two functions returned anything. What do I have wrong?

1. Think about what the main method does.
2. Create static methods initList(List<Number> list), printListValues(List<Number> list), and processCastObjects(List<Number> list) in the Solution class.
3. Find the block of code that fills the list with values and move it to the initList method.
4. Find the block of code that uses a for loop to display the contents of the list, and move it to the printListValues method.
5. Find the block of code that checks the type of each object of the list and displays messages on the screen, and move it to the processCastObjects method.
6. Correct 2 bugs in the printListValues method so that the method correctly displays the contents of the list passed as an argument.
7. Correct 2 bugs related to type casting in the processCastObjects method
- for a Float object, you need to display "Is float defined? " + !(<Float object>.isNaN()).
- for a Double object, you need to print "Is double infinite? " + <Double object>.isInfinite().

Requirements:

The Solution class must implement static methods initList(List<Number> list), printListValues(List<Number> list), and processCastObjects(List<Number> list).
The initList method must fill the resulting list with random values.
The printListValues method should display the contents of the resulting list.
The processCastObjects method should analyze the list items and display text for Float and Double objects in accordance with the task conditions.

package com.codegym.task.task14.task1418; import java.util.LinkedList; import java.util.List; /* Fix four mistakes */ public class Solution { public static void main(String[] args) { List<Number> list = initList(new LinkedList<Number>()); printListValues(list); processCastObjects(list); } public static List<Number> initList(List<Number> list) { list.add(new Double(1000f)); list.add(new Double("123e-445632")); list.add(new Float(-90 / -3)); list.remove(new Double("123e-445632")); return list; } public printListValues(List<Number> list){ for (Number object : list) { // Correct 2 bugs if (object instanceof Float) { Double a = (Double) object; System.out.println("Is float defined? " + !(a.isNaN())); } else if (object instanceof Double) { Float a = (Float) object; System.out.println("Is double infinite? " + a.isInfinite()); } } //return list; } public processCastObjects(List<Number> list){ // 4 - Correct 2 bugs for (int i = 0; i < list.size(); i++) { System.out.println(list.get(i)); } //return list; } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

12 August 2020, 14:30

All methods need to have at minimum 2 things to be valid: A name and a return type. Without these 2 a method is not valid. The optional parts of a method are the access modifier (public, private, protected), the static modifier, and the arguments. So, a correct method would look something like these:

// access modifier: public, static included, return type: void, name: method 1, args: none
public static void method1() {

}

// no access modifier, not static, return type: Integer, name: method2, args: int, string
Integer method2(int x, String name) {
   //must return an Integer
}

//access: protected, static, return type: ArrayList<Integer>, name: Method3, args: List<Number>
protected static ArrayList<Integer> method3(List<Number> list){
   //must return an ArrayList<Integer>
}

Maxine Hammett

Level 19 , San Diego, United States

13 August 2020, 15:42

I tried to fix my method using the template you provided, but I get an error on the return type.

public static ArrayList<Number> printListValues(List<Number> list){
    for (Number object : list) {
        // Correct 2 bugs
        if (object instanceof Float) {
            Double a = (Double) object;
            System.out.println("Is float defined? " + !(a.isNaN()));
        } else if (object instanceof Double) {
            Float a = (Float) object;
            System.out.println("Is double infinite? " + a.isInfinite());
        }
    }
    return list<object>;
}

Guadalupe Gagnon

Level 37 , Tampa, United States

13 August 2020, 17:13

I would ask you why you chose ArrayList<Number> as the return value? Is there a specific reason or was it thrown in there just because? You have to remember that computers, while being able to handle a lot of complex tasks quite efficiently, still do only EXACTLY what the programmer tells them to do. At this point in your learning I would definitely encourage you to experiment and try different things out, right or wrong, but also try to do things purposefully, meaning not just throwing in random fillers just because. Looking at this method I can see the work that it is doing is iterating through a list passed in as an argument, then outputting a line of text for each value in the list. It does nothing further, no adding, removing, or modification of the values contained within the list; it also does not create a second List<object> that it fills with values. With this in mind, to me, this method would seem self contained and require no return value.

Guadalupe Gagnon

Level 37 , Tampa, United States

13 August 2020, 17:16

P.S.

return List<object>;

is an invalid/incomplete statement. It would be akin to saying a partial sentence to express a complete idea. A valid way would be:

List<Object> tempList = new ArrayList<>();
return tempList;

/* or */

return new ArrayList<Object>();

dhanush

Level 30 , Chennai, India

12 August 2020, 14:21

solution

Look at the line 26 and 39 there is the bug. every method must have <modifier><static><return type><method name>(){}

Maxine Hammett

Level 19 , San Diego, United States

13 August 2020, 17:16

I got it working! Having the <modifier><static><return type><method name>(){} was exactly the hint I needed. Thank you