java - 对象数组出现问题

当我尝试运行此方法时，出现了空指针异常，目标是填充书本对象数组，但不超过3个对象。当我设置booklist [0] = b时发生错误

private Book [] booklist;
public boolean borrowBook(Book b)
{
    if(booklist == null)
    {
        booklist[0] = b;
        System.out.println(this.name+" has successfully borrowed "+b);
        return true;
    }
    if(booklist.length < 3)
    {
        booklist[booklist.length] = b;
        System.out.println(this.name+" has successfully borrowed "+b);
        return true;
    }
    System.out.println(this.name+" has reached the borrowing limit! Return those books "+this.name);
    return false;

最佳答案

试试这个。

private Book [] booklist;

public boolean borrowBook(Book b) {
    if (booklist == null) {
        booklist = new Book[3];
        booklist[0] = b;
        return true;
    }
    for (int i = 0; i < booklist.length; i++) {
        if (booklist[i] == null) {
            booklist[i] = b;
            return true;
        }
    }
    return false;
}

public static void main(String[] args) {
    Book caller = new Book();
    System.out.println(caller.borrowBook(new Book()));
    System.out.println(caller.borrowBook(new Book()));
    System.out.println(caller.borrowBook(new Book()));
    System.out.println(caller.borrowBook(new Book()));
}

关于java - 对象数组出现问题，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/26133031/