Java找不到符号get.Method，但声明了Method

Question

I was given this class and told to fix errors and Finnish the class.

For this assignment, you will need to develop a test driver and a comparable class. Luckily, Prof. Fuller has such class already written (well most of it), you just need to add some code and debug some errors. This is what I have as well as what was given.

public class Jedi implements Comparable {

    private String name;
    private double midi;

    public Jedi(String name, double midi) {
        this.name = name;
        this.midi = midi;
    }

    public Jedi(String name) {
        this.name = name;
        this.midi = -1;
    }

    public String toString() {
        return "Jedi " + name + "\nMidi-chlorians count : " + midi + "\n";
    }

    public double getMidi() {
        return midi;
    }

    public String getName() {
        return name;
    }

    // returns true if the object’s midi value are equal and false otherwise – CODE INCOMPLETE
    public boolean equals(Jedi other) {
        return this.getMidi() == other.getMidi();
    }

    // returns -1 if less, 1 if larger, or 0 if it is an equal midi count – CODE INCOMPLETE
    public int compareTo(Object other) {
        if (getMidi() < other.getMidi()) {
            return -1;
        } else if (getMidi > other.getMidi()) {
            return 1;
        } else if (this.equals(other)) {
            return 0;
        }
    }
}

I keep getting a cannot find symbol - method getMidi()

What is wrong with this because I can not figure it out?

Answer 1

This is the problem:

public int compareTo(Object other)

You've said you can compare this object to any other object . You can't call other.getMidi() , because getMidi() isn't a method declared on Object .

I would suggest you change your class and method declarations to use the fact that Comparable<T> is generic:

public class Jedi implements Comparable<Jedi> {
    ...
    public int compareTo(Jedi other) {
        ...
    }
}

Answer 2

Your problem is here:

public int compareTo(Object other)
{
    if (getMidi() < other.getMidi())
        return -1;
    else if (getMidi > other.getMidi())
        return 1;
    else if (this.equals(other))
        return 0;
}

other is an Object . An Object does not have a getMidi() method. Change it to:

public int compareTo(Jedi other)
{
    if (getMidi() < other.getMidi())
        return -1;
    else if (getMidi > other.getMidi())
        return 1;
    else if (this.equals(other))
        return 0;
}

Answer 3

1. Object does not have a getMidi() method.

2. What if all the if conditions are not met, what is returned? So please correct that. As in

       public int compareTo(Object other) {

            if (getMidi() < other.getMidi()) {
                return -1;
            } else if (getMidi > other.getMidi()) {
                return 1;
            } else if (this.equals(other)) {
                return 0;
            }
            return ....Something if conditions are not met.
        }

Answer 4

You are trying to use the methods that you defined for the Jedi class in the Object class, this can not work. If you need to manage an object that has an Object type (you have to be sure about its type before to cast it), before to use it you have to cast it to the expected object type (Jedi for this example).

So, your code would be similar to the following one:

public class Jedi implements Comparable {
    private String name;
    private double midi;

    public Jedi(String name, double midi) {
        this.name = name;
        this.midi = midi;
    }

    public Jedi(String name) {
        this.name = name;
        this.midi = -1;
    }

    public String toString() {
        return "Jedi " + name + "\nMidi-chlorians count : " + midi + "\n";
    }

    public double getMidi() {
        return midi;
    }

    public String getName() {
        return name;
    }

    // returns true if the object’s midi value are equal and false otherwise – CODE INCOMPLETE
    public boolean equals(Jedi other) {
        return this.getMidi() == other.getMidi();
    }

    // returns -1 if less, 1 if larger, or 0 if it is an equal midi count – CODE INCOMPLETE
    public int compareTo(Object other) {
        if (getMidi() < ((Jedi)(other)).getMidi()) {
            return -1;
        } else if (getMidi() > ((Jedi)(other)).getMidi()) {
            return 1;
        } else if (this.equals(other)) {
            return 0;
        }
        return -1; // !!! YOU DID NOT PROVIDE THIS CASE !!!
    }
}

Please note that your compareTo() function contains an error, you do not provide a return statement for the main else branch.