java.lang.NullPointerException异常问题解决方案

/**
    *  引用类型变量没有指向对象所引起的空指针异常
 * @author Superhero
 * @version 2018年12月16日上午10:32:43
 */
 //图书类
class Books
{
 private String name;
 private String author;
 private double price;
 
 public Books()
 {
  
 }
 
 public Books(String name, String author, double price)
 {
  this.name = name;
  this.author = author;
  this.price = price;
 }
 
 public String getName()
 {
  return name;
 }
 
 public String getAuthor()
 {
  return author;
 }
 
 public double getPrice()
 {
  return price;
 }
}

//启动类
public class NullPointerExceptionTest1
{
 public static void main(String[] args)
 {
  Books book=null;
  //下面一行代码会报指针异常错误：
    System.out.println("name:"+book.getName()+", author:"+book.getAuthor()+",    price:"+book.getPrice());
 }
}

public class NullPointerExceptionTest2
{
 public static void main(String[] args)
 {
  Books[] books = new Books[3];
  books[0] = new Books("NullPointerException","Superhero",88.8);
    //books[1],book[2]没有指向对象，所以也报空指针异常
  for(Books book : books)
   System.out.println("name:"+book.getName()+", author:"+book.getAuthor()+", price:"+book.getPrice());
 }
}