在hashset中复制元素(在正确实现comparator /compare方法之后)

Question

我目前正在编写一个程序，从文件中读取行并创建令牌。然后将令牌保存在treeset中。我不希望在集合中有任何重复项，所以我用正确的比较方法实现了Comparator。但是我还是不明白为什么有一个元素在树集中重复出现。

输入文件:(13行)

VEG,SMALL,Corn,MOZZARELLA 
VEG,LARGE,Capsicum,CHEDDAR 
VEG,MEDIUM,Olives,COTTAGE 
VEG,MEDIUM,Garlic,MOZZARELLA 
VEG,LARGE,Peppers,CHEDDAR     
NONVEG,MEDIUM,Beef,CHEDDAR  
NONVEG,LARGE,Chicken,COTTAGE  
NONVEG,SMALL,Pork,MOZZARELLA  
NONVEG,LARGE,Mutton,CHEDDAR    
NONVEG,SMALL,Mutton,MOZZARELLA 
VEG,SMALL,Corn,MOZZARELLA
NONVEG,MEDIUM,Beef,CHEDDAR 
NONVEG,SMALL,Mutton,MOZZARELLA  

My Code:

public Set<Pizza> populateData(String FileName) {
    Set<Pizza> set = new TreeSet(new Comparator<Pizza>(){
        @Override
        public int compare(Pizza o1, Pizza o2) {
            if(o1.getPizzType().compareTo(o2.getPizzType())==0)
            {
                if(o1.getCheeseType().compareTo(o2.getCheeseType())==0)
                {
                    if(o1.getSize().compareTo(o2.getSize())==0)
                    {
                        if(o1.getTopping().compareTo(o2.getTopping())==0)
                        {
                            return 0;
                        }
                    }
                }
            }
            return 54;
        }

    });

    File file = new File(FileName);
    Scanner scanner=null;
    try {
        scanner=new Scanner(new FileInputStream(file));
        Pizza pizza=null;
        while(scanner.hasNext())
        {
            String line=scanner.nextLine();
            String words[]=new String[4];
            words=line.split(",");
            pizza=new Pizza();
            if(words[0].trim().length()>0)
            {
                pt=PizzaType.valueOf(words[0].trim());
                pizza.setPizzType(PizzaType.valueOf(words[0].trim()));
            }
            if(words[1].trim().length()>0)
            {
                sz=(Size.valueOf(words[1].trim()));
                pizza.setSize(Size.valueOf(words[1].trim()));
            }
            if(words[2].trim().length()>0)
            {
                tp=(words[2].trim());
                pizza.setTopping(words[2].trim());
            }
            if(words[3].trim().length()>0)
            {
                ct=(CheeseType.valueOf(words[3].trim()));
                pizza.setCheeseType(CheeseType.valueOf(words[3].trim()));
            }

            set.add(pizza);
        }
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return set;
}

(输出与字符串长度和哈希码一起打印)

输出:(11行){第一行和最后一行重复:p}

VEG SMALL Corn MOZZARELLA 22  589431969
VEG LARGE Capsicum CHEDDAR 23  1252169911
VEG MEDIUM Olives COTTAGE 22  2101973421
VEG MEDIUM Garlic MOZZARELLA 25  685325104
VEG LARGE Peppers CHEDDAR 22  460141958
NONVEG MEDIUM Beef CHEDDAR 23  1163157884
NONVEG LARGE Chicken COTTAGE 25  1956725890
NONVEG SMALL Pork MOZZARELLA 25  356573597
NONVEG LARGE Mutton CHEDDAR 24  1735600054
NONVEG SMALL Mutton MOZZARELLA 27  21685669
VEG SMALL Corn MOZZARELLA 22  2133927002

期望输出:(10行)

VEG SMALL Corn MOZZARELLA  
VEG LARGE Capsicum CHEDDAR
VEG MEDIUM Olives COTTAGE 
VEG MEDIUM Garlic MOZZARELLA
VEG LARGE Peppers CHEDDAR 
NONVEG MEDIUM Beef CHEDDAR 
NONVEG LARGE Chicken COTTAGE
NONVEG SMALL Pork MOZZARELLA
NONVEG LARGE Mutton CHEDDAR 
NONVEG SMALL Mutton MOZZARELLA

Answer 1

比较器契约要求如果o1 < o2返回负，如果o1 > o2返回正，如果o1 == o2返回零。

这意味着你的代码需要看起来像

public int compare(Pizza o1, Pizza o2) {
    int compvalue = o1.getPizzType().compareTo(o2.getPizzType());
    if(compvalue == 0)
    {
        compvalue = o1.getCheeseType().compareTo(o2.getCheeseType());
        ...etc..
        if(compvalue == 0)
        ...
    }
    return compvalue;
}