JAVAlang.NullPointerException:null
基本上我有一个图书馆系统
private int numberOfBooks = 0;
public int getNumberOfBooks()
{
return numberOfBooks;
}
当然,当你在图书馆增加一本新书时,书的数量会增加1。我的另一个班的学生有以下代码:
private LibrarySystem libraryBooks;
public void searchByISBN()
{
int i = 0;
boolean found = false;
while(i<libraryBooks.getNumberOfBooks()) //THE PROBLEM IS HERE
{
if(books[i].getISBN().equals(in.next()))
{
found = true;
break;
}
i++;
}
if(found)
{
System.out.println("\n Book info: \n ISBN: " + books[i].getISBN() +
"\n Title: " + books[i].getTitle() +
"\n Author: " + books[i].getAuthor() +
"\n Subject: " + books[i].getSubject());
}
else System.out.println("There is no book with such ISBN");
}
我有一个Java。我不知道为什么。我该怎么解决这个问题
# 1 楼答案
在函数中,输入以下内容:
因为您尚未初始化它,
libraryBooks
为空