Question

我收到此错误；二进制运算符'-'的错误操作数类型。它发生在网上；

- p2.getProductNum();

如果有人可以帮助解决此异常，将不胜感激。

BetterBasket类

package catalogue;
import java.io.Serializable;
import java.util.Collections;
import java.util.Comparator;

/**
 * @version 1.0
 */
public class BetterBasket extends Basket implements Serializable
{
    private static final long serialVersionUID = 1L;
    @Override
    public boolean add( Product pr )
    { 
        super.add(pr);
        Collections.sort(this, new Comparator<Product>() {
                @Override
                public int compare(Product p1, Product p2) {
                    return p1.getProductNum() - p2.getProductNum();
                }
            });
        }
    }

产品类别

package catalogue;

import java.io.Serializable;

/**
 * Used to hold the following information about
 * a product: Product number, Description, Price and
 * Stock level.
 */

public class Product implements Serializable
{
  private static final long serialVersionUID = 20092506;
  private String theProductNum;       // Product number
  private String theDescription;      // Description of product
  private double thePrice;            // Price of product
  private int    theQuantity;         // Quantity involved

  /**
   * Construct a product details
   * @param aProductNum Product number
   * @param aDescription Description of product
   * @param aPrice The price of the product
   * @param aQuantity The Quantity of the product involved
   */
  public Product( String aProductNum, String aDescription,
                  double aPrice, int aQuantity )
  {
    theProductNum  = aProductNum;     // Product number
    theDescription = aDescription;    // Description of product
    thePrice       = aPrice;          // Price of product
    theQuantity    = aQuantity;       // Quantity involved
  }

  public String getProductNum()  { return theProductNum; }
  public String getDescription() { return theDescription; }
  public double getPrice()       { return thePrice; }
  public int    getQuantity()    { return theQuantity; }

  public void setProductNum( String aProductNum )
  { 
    theProductNum = aProductNum;
  }

  public void setDescription( String aDescription )
  { 
    theDescription = aDescription;
  }

  public void setPrice( double aPrice )
  { 
    thePrice = aPrice;
  }

  public void setQuantity( int aQuantity )
  { 
    theQuantity = aQuantity;
  }

}

篮子课

package catalogue;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Currency;
import java.util.Formatter;
import java.util.Locale;

/**
 * A collection of products from the CatShop.
 *  used to record the products that are to be/
 *   wished to be purchased.
 *
 */
public class Basket extends ArrayList<Product> implements Serializable
{
  private static final long serialVersionUID = 1;
  private int    theOrderNum = 0;          // Order number

  /**
   * Constructor for a basket which is
   *  used to represent a customer order/ wish list
   */
  public Basket()
  {
    theOrderNum  = 0;
  }

  /**
   * Set the customers unique order number
   * Valid order Numbers 1 .. N
   * @param anOrderNum A unique order number
   */
  public void setOrderNum( int anOrderNum )
  {
    theOrderNum = anOrderNum;
  }

  /**
   * Returns the customers unique order number
   * @return the customers order number
   */
  public int getOrderNum()
  {
    return theOrderNum;
  }

  /**
   * Add a product to the Basket.
   * Product is appended to the end of the existing products
   * in the basket.
   * @param pr A product to be added to the basket
   * @return true if successfully adds the product
   */
  // Will be in the Java doc for Basket
  @Override
  public boolean add( Product pr )
  {                              
    return super.add( pr );     // Call add in ArrayList
  }

  /**
   * Returns a description of the products in the basket suitable for printing.
   * @return a string description of the basket products
   */
  public String getDetails()
  {
    Locale uk = Locale.UK;
    StringBuilder sb = new StringBuilder(256);
    Formatter     fr = new Formatter(sb, uk);
    String csign = (Currency.getInstance( uk )).getSymbol();
    double total = 0.00;
    if ( theOrderNum != 0 )
      fr.format( "Order number: %03d\n", theOrderNum );

    if ( this.size() > 0 )
    {
      for ( Product pr: this )
      {
        int number = pr.getQuantity();
        fr.format("%-7s",       pr.getProductNum() );
        fr.format("%-14.14s ",  pr.getDescription() );
        fr.format("(%3d) ",     number );
        fr.format("%s%7.2f",    csign, pr.getPrice() * number );
        fr.format("\n");
        total += pr.getPrice() * number;
      }
      fr.format("----------------------------\n");
      fr.format("Total                       ");
      fr.format("%s%7.2f\n",    csign, total );
      fr.close();
    }
    return sb.toString();
  }
}

Answer 1

替换此行：

return p1.getProductNum() - p2.getProductNum();

使用

p1.getProductNum().compareTo(p2.getProductNum());

p1.getProductNum()和p2.getProductNum()都是字符串，您不能将它们相减。
您想比较它们，因为您需要创建一个Comperator用于对Collection个对象中的Product进行排序。

Answer 2

getProductNum()返回一个字符串。

如果出于任何原因想要将此字符串保留为字符串，则可以使用：

p1.getProductNum().compareTo(p2.getProductNum());

如果不需要字符串，请更改：

private String theProductNum;

收件人：

`private int theProductNum;` and make sure the method returns an int :)

二进制运算符的错误操作数-两种类型

2 个答案: