java - 引用对象数组时，Java NullPointerException

我有以下程序：

class Books
{
    String title;
    String author;
}

class BookTestDrive
{
    public static void main(String [] args)
    {
        Books [] myBooks = new Books[3];
        int x = 0;
        myBooks[0].title = "The Grapes of Java";
        myBooks[1].title = "The Java Gatsby";
        myBooks[2].title = "The Java Cookbook";
        myBooks[0].author = "bob";
        myBooks[1].author = "sue";
        myBooks[2].author = "ian";

        while (x < 3)
        {
            System.out.print(myBooks[x].title);
            System.out.print(" by ");
            System.out.println(myBooks[x].author);
            x = x + 1;
        }
    }
}

但是，执行该命令时会出现以下错误：

Exception in thread "main" java.lang.NullPointerException
    at BookTestDrive.main(Books.java:14)

我是Java新手。从我的C / C ++经验来看，代码看起来是合法的...如何解决此问题？

最佳答案

问题是您仅在以下几行中创建了一系列图书：

Books [] myBooks = new Books[3];

在访问它们之前，您仍然需要将数组中的每个元素初始化为book对象。

示例代码如下所示：

Books [] myBooks = new Books[3];
int x = 0;
myBooks[0] = new Books();
myBooks[0].title = "The Grapes of Java";

您需要对数组中的所有元素执行此操作。