有人知道我在执行这个 java 代码时做错了什么吗？

Question

I am just trying to execute some Java code and print them out to the console, however, when I try to run it, it gives an error and says illegal start to expression. Does anyone know what is going on here?

    package com.craneai;

public class Main {

    public static void main(String[] args) {

        public static void int F(int N) {
            int X, Y, Z, I;

            int X = 2;
            if(N <= 0) {
                X = 3;
            } else {
                Y = 1;
                Z = 1;
                for (int I = 3; I <=N; I++) {
                    X = Y + Z;
                    Z = Y;
                    Y = X;
                }
            }
            return X;
        }


        System.out.println(F(6));
        System.out.println(F(0));
        System.out.println(F(1));

    }



}

Answer 1

public static void main(String[] args) {


        System.out.println(F(6));
        System.out.println(F(0));
        System.out.println(F(1));

    }

    public static int F(int N) {
        int X, Y, Z, I;

        X = 2;
        if(N <= 0) {
            X = 3;
        } else {
            Y = 1;
            Z = 1;
            for (int i = 3; i <=N; i++) {
                X = Y + Z;
                Z = Y;
                Y = X;
            }
        }
        return X;
    }

A few things to consider:

1st. You're declaring a void return and then a int, the function must have only 1 return type.

public static void int F(int N)

2nd. The method should be outside the main method

3rd. You declared X twice in the code, the second time you call it, you don't have to declare the type, the compiler will try to process it as a new variable with a name that is already in use.

4th. In your for method, you declared X , once again, Java is case sensitive, so X and x are different in the compiler.

5th. You've also declared I twice, you don't need to provide a temporary variable before calling the for method, since you can do it inside the for loop;

Looks like you're starting to learn Java, a few tips from who works with it since the Java 5..

• Don't declare your variables with a single letter;
• Don't declare your functions/methods with a single letter;
• Don't declare your variables in UPPER CASE, always low case and camelCase;

Even as an example you should make your code cleaner, improve the readability for others, other people will be happier in the future if you do this (this include yourself).

Answer 2

First: you're declaring a method inside another method - see that the F method is inside the main method. Java does not support nested methods.

Second: you're declaring X and I twice.

Third: You wrote two return types to your method: void and int .

This will work:

public class Main {

    public static void main(String[] args) {
        System.out.println(F(6));
        System.out.println(F(0));
        System.out.println(F(1));
    }

    public static int F(int N) {
        int X, Y, Z, I;

        X = 2;
        if (N <= 0) {
            X = 3;
        } else {
            Y = 1;
            Z = 1;
            for (I = 3; I <= N; I++) {
                X = Y + Z;
                Z = Y;
                Y = X;
            }
        }
        return X;
    }

}

Answer 3

Three main errors:

1. Nested method: F method inside main
2. Method F return int and void
3. You declared X and I twice.

Here is your class fixed:

public class Main {
    
        public static void main(String[] args) {
            System.out.println(F(6));
            System.out.println(F(0));
            System.out.println(F(1));
    
        }
    
        public static int F(int N) {
            int X = 2, Y, Z;
    
            if (N <= 0) {
                X = 3;
            } else {
                Y = 1;
                Z = 1;
                for (int I = 3; I <= N; I++) {
                    X = Y + Z;
                    Z = Y;
                    Y = X;
                }
            }
            return X;
        }
    }

Output is going to be this:

8
3
2