main方法启动nothing here

如果你在打开Jar包并查看其中的代码后发现没有找到`main`方法，那可能有几种原因：

1. 代码中确实没有定义`main`方法：`main`方法是Java程序的入口点，如果代码中没有定义`main`方法，那么程序将无法直接运行。

2. `main`方法可能位于其他类中：在Java程序中，`main`方法可以位于任何类中，但是只能有一个`main`方法作为程序的入口点。你可以尝试搜索其他类并查看是否有定义了`main`方法。

3. Jar包可能是一个库或框架：有些Jar包是用于提供功能或服务的库文件，它们通常不包含可直接执行的代码。这种情况下，你需要查阅对应的文档或示例来了解如何使用该库。

如果你可以提供更多关于Jar包的信息，比如它是用来做什么的或者你期望它能够执行什么功能，我可以给出更具体的建议。

相关问题

The constructor of the ViewSimple class registers the view with the model (the library) using the addListener method of the model, creates a JLabel object, stores it in the label instance variable of the ViewSimple class, initializes it to display the total number of books borrowed by all users of the library, and adds the label to the view (which is a frame). The update method of the ViewSimple class updates the text of the label as necessary so that the label always displays the current value of the total number of books borrowed by all users of the library. Since the ViewSimple does not have any button, it cannot perform any action, therefore the corresponding controller ControllerSimple does nothing. (We still want to have the ControllerSimple class so that our application follows the correct Model-View-Controller design pattern.) Fifth, create a GUI class with a main method. In this main method, create an anonymous class that implements the Runnable interface with a run method and use the javax.swing.SwingUtilities.invokeLater method to run that code on the event dispatch thread.

This GUI class should create an instance of the ModelSimple, an instance of the ViewSimple, and an instance of the ControllerSimple. Then, it should register the view with the model by calling the addListener method of the model and passing in the view as a parameter. Finally, it should set the size of the view and make it visible. Here's an example code:

public class LibraryGUI {
    public static void main(String[] args) {
        ModelSimple model = new ModelSimple();
        ViewSimple view = new ViewSimple();
        ControllerSimple controller = new ControllerSimple(model, view);

        model.addListener(view);
        
        JFrame frame = new JFrame("Library");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(view);
        frame.pack();
        frame.setVisible(true);

        // run the code on the event dispatch thread
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                // update the view periodically
                while (true) {
                    try {
                        Thread.sleep(1000); // wait for 1 second
                    } catch (InterruptedException e) {}
                    model.update(); // update the model
                }
            }
        });
    }
}

This code creates an infinite loop that periodically updates the model and the view. You can modify the frequency of the updates by changing the value of the sleep time. Note that this is just a simple example to demonstrate the basic structure of a Model-View-Controller application. In practice, you would typically use event listeners to trigger updates instead of polling the model periodically.

Write a C function named isPrime that checks whether a given number is a prime or not. Include the fuction isPrime in a working program to verify Goldbach's Conjecture: Every even number greater than 4 can be written as the sum of two odd prime numbers. Make sure the function isPrime is called from the main method, and correctly returns a value to the main method.

Sure, here is a C program that includes the `isPrime` function to verify Goldbach's Conjecture:

#include <stdio.h>

int isPrime(int num);

int main() {
    int num, i, j;
    
    printf("Enter an even number greater than 4: ");
    scanf("%d", &num);
    
    if (num <= 4 || num % 2 != 0) {
        printf("Invalid input!\n");
        return 0;
    }
    
    for (i = 3; i <= num / 2; i += 2) {
        if (isPrime(i) && isPrime(num - i)) {
            printf("%d = %d + %d\n", num, i, num - i);
        }
    }
    
    return 0;
}

int isPrime(int num) {
    int i;
    
    if (num < 2) {
        return 0;
    }
    
    for (i = 2; i <= num / 2; i++) {
        if (num % i == 0) {
            return 0;
        }
    }
    
    return 1;
}

The `isPrime` function takes an integer as input and returns 1 if the number is prime, and 0 otherwise. The `main` function prompts the user to enter an even number greater than 4, and then checks whether the input is valid. If the input is valid, the program uses a for loop to check all odd prime numbers less than or equal to half of the input number. For each odd prime number `i`, the program checks whether the difference between the input number and `i` is also a prime number. If both numbers are prime, the program prints out the input number as the sum of `i` and the difference between the input number and `i`. If no such pairs of prime numbers are found, the program prints nothing. The `isPrime` function is called from the `main` function to check whether each number is prime.