java - 阵列标价

Question

我正在尝试创建一个价格低于给定数字的书籍数组列表，并且我不断收到此编译器错误:

   JAmos_Chapter09_exercise_94Arrays.java:86: error: double cannot be dereferenced
   if ( ( currentJAmos_Chapter09_exercise_94.getPrice( ) ).indexOf( searchString ) != -1 )
                                                               ^
1 error

在我的数组列表文件的代码中编译此方法后:

 public ArrayList<JAmos_Chapter09_exercise_94> searchForPrice( String searchString )
 {
  ArrayList<JAmos_Chapter09_exercise_94> searchResult = new ArrayList<JAmos_Chapter09_exercise_94>( );
  for ( JAmos_Chapter09_exercise_94 currentJAmos_Chapter09_exercise_94 : library )
  {
   if ( ( currentJAmos_Chapter09_exercise_94.getPrice( ) ).indexOf( searchString ) != -1 )
        searchResult.add( currentJAmos_Chapter09_exercise_94 );
  }
  searchResult.trimToSize( );
  return searchResult;
 }

我的方法代码的 getPrice 部分从此类文件中获取 double 值:

 /** default constructor
 */
 public JAmos_Chapter09_exercise_94( )
 {
  title = "";
  author = "";
  price  = 0.0;
 }

 /** overloaded constructor
 *  @param newTitle   the value to assign to title
 *  @param newAuthor  the value to assign to author
 *  @param newPrice   the value to assign to price
 */
 public JustinAmos_Chapter09_exercise_94( String newTitle, String newAuthor, double newPrice )
 {
  title = newTitle;
  author = newAuthor;
  price  = newPrice;
 }

 /** getTitle method
 *   @return the title
 */
 public String getTitle( )
 {
  return title;
 }

 /** getAuthor method
 *   @return the author
 */
 public String getAuthor( )
 {
  return author;
 }

 /** getPrice method
 *   @return the price
 */
 public double getPrice( )
 {
  return price;
 }

 /** toString
 * @return title, author, and price
 */
 public String toString( )
 {
  return ( "title: " + title + "\t"
           + "author: " + author + "\t"
           + "price: " + price );
 }
}

总的来说，我想知道如何摆脱

double cannot be dereferenced error

因为我需要搜索 double 而不是字符串。

抱歉，如果这篇文章太长了。

Answer 1

不要使用.indexOf()查找价格是否低于某个值。 .indexOf(s)查找另一个字符串中某个字符串的第一个实例的起始索引。

您正在寻找小于比较运算符:< .

将逻辑更改为:

public ArrayList<JAmos_Chapter09_exercise_94> searchForPrice( String searchString ) {  
  ArrayList<JAmos_Chapter09_exercise_94> searchResult = new ArrayList<JAmos_Chapter09_exercise_94>( ); 
  //Converts the search string price into a double price.
  double maxPrice = Double.parseDouble(searchString);
  for ( JAmos_Chapter09_exercise_94 currentJAmos_Chapter09_exercise_94 : library ) {
    //If itemPrice < maxPrice, add it to the list.
    if ( currentJAmos_Chapter09_exercise_94.getPrice( ) < maxPrice)
      searchResult.add( currentJAmos_Chapter09_exercise_94 );
  } 
  searchResult.trimToSize( ); 
  return searchResult; 
}

如果您的searchString不是一个格式良好的 double ，我建议编写一个例程来转换 searchString变成双。

编辑:如果不清楚，请在评论中询问我......