将主类连接到其他类

Question

我正在用java编写一个程序，如果我必须创建一个包含main和第二个类（Invoice）的类（InvoiceTest）。当我运行主InvoiceTest类时，它应该在Invoice类中显示消息。我一直收到错误

Exception in thread "main" java.lang.ExceptionInInitializerError
    at InvoiceTest.main(InvoiceTest.java:4)
Caused by: java.lang.RuntimeException: Uncompilable source code - constructor Invoice() is already defined in class Invoice
    at Invoice.<clinit>(Invoice.java:20)
    ... 1 more

我不知道该怎么办，请让我知道我做错了什么，以及如何解决它的任何建议。谢谢

public class InvoiceTest{
    public static void main(String [] args) {
        Invoice invoiceObject = new Invoice();
        invoiceObject.simpleMessage();
    }
}
// This is the second class. I am using NetBeans so each class is in its own window.
public class Invoice {        
    public void simpleMessage() {
        System.out.println("This is another class");
    }
}

Answer 1

您不需要两个单独的类。一节课有效。

public class Invoice {        
    public void simpleMessage() {
        System.out.println("This is another class");
    }
    public static void main(String[] args) {
        Invoice invoiceObject = new Invoice();
        invoiceObject.simpleMessage();
    }
}

Answer 2

它们是否都在同一个.java文件中？java编译器要求每个源文件只有一个java类。

Answer 3

确实是一个奇怪的错误。

如何添加回类Invoice的构造函数？

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