Java 为什么我的排序函数会产生如此不寻常的输出?
我有一个程序,它从一个csv文件中读取所有人的姓、名和出生年份,将他们分配到一个特殊的类数组中,然后根据他们的姓进行排序。我相信我的代码是有效的,所以我所要做的就是验证输出列表,看看是否所有的人都是按姓氏排序的。但是,我很难找到正确的语法来执行此操作。 下面是Main.java的代码,我认为问题一定出在这里Java 为什么我的排序函数会产生如此不寻常的输出?,java,class,sorting,comparator,comparable,Java,Class,Sorting,Comparator,Comparable,我有一个程序,它从一个csv文件中读取所有人的姓、名和出生年份,将他们分配到一个特殊的类数组中,然后根据他们的姓进行排序。我相信我的代码是有效的,所以我所要做的就是验证输出列表,看看是否所有的人都是按姓氏排序的。但是,我很难找到正确的语法来执行此操作。 下面是Main.java的代码,我认为问题一定出在这里 package project_1_sorting; import java.io.BufferedReader; import java.io.FileReader; import j
package project_1_sorting;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Main
{
public static void main(String[] args) throws IOException {
// open file input stream
BufferedReader reader = new BufferedReader(new FileReader(
"C:\\Users\\Owner\\Desktop\\Data 18k.csv")); // double check where this is trying to read it from
// read file line by line
String line = null;
Scanner scanner = null;
int index = 0;
Human[] pplArray = new Human[18000];
int i = 0;
while ((line = reader.readLine()) != null) {
Human ppl = new Human();
scanner = new Scanner(line);
scanner.useDelimiter(",");
while (scanner.hasNext()) {
String data = scanner.next();
if (index == 0)
ppl.setLastName(data);
else if (index == 1)
ppl.setFirstName(data);
else if (index == 2)
ppl.setBirthYear(data);
else
System.out.println("invalid data::" + data);
index++;
}
ppl.setKey(0); //change this for later things, you can use loop
ppl.setOrder(0); //change this to 1 if you want to invert the list of people
index = 0;
pplArray[i] = ppl;
i++;
System.out.println(pplArray);
}
//close reader
reader.close();
System.out.println(pplArray); // create
Selection_Sort selection = new Selection_Sort();
for (int j = 0; j < 18000; j++)
{
System.out.println(pplArray[j]);
}
}
}
我注意到的一件事是最后一行
Selection_Sort selection = new Selection_Sort();
它说“不使用变量选择”
我认为这是在说我没有正确地使用我的选择排序。我正在创建该类的对象,但没有使用它
以下是我的选择_Sort.java:
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package project_1_sorting;
public class Selection_Sort
{
public static void sort(Comparable[] a)
{ // Sort a[] into increasing order.
int N = a.length; // array length
for (int i = 0; i < N; i++)
{ // Exchange a[i] with smallest entry in a[i+1...N).
int min = i; // index of minimal entr.
for (int j = i+1; j < N; j++)
if (less(a[j], a[min])) min = j;
exch(a, i, min);
}
}
// See page 245 for less(), exch(), isSorted(), and main()
private static boolean less(Comparable v, Comparable w)
{
return v.compareTo(w) < 0;
}
private static void exch(Comparable[] a, int i, int j)
{
Comparable t = a[i]; a[i] = a[j]; a[j] = t;
}
}
但是,第二行代码会创建一条错误消息:
'.class' expected
cannot find symbol
symbol: class pplArray
location : class main
如果我移除pplArray上的支架:
Selection_Sort selection = new Selection_Sort();
selection.sort(pplArray);
错误消息更改为
incompatible types: Human[] cannot be converted to Comparable
这让我想知道我的Human类是否有什么问题,下面是我的Human.java:
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package project_1_sorting;
class Human{
String firstName;
String lastName;
String birthYear;
int Key;
int Order;
public Human() // A constructor
{
}
public int compareTo(Human person)
{
if (Order == 0)
{
if (Key == 0)
return lastName.compareTo(person.lastName );
else if (Key == 1)
return firstName.compareTo(person.firstName );
else
return birthYear.compareTo(person.birthYear );
}
else
{
if (Key == 0)
return (lastName.compareTo(person.lastName ) ) * -1;
else if (Key == 1)
return ( firstName.compareTo(person.firstName ) ) * -1;
else
return ( birthYear.compareTo(person.birthYear ) ) * -1;
}
}
public void printHuman ()
{
StdOut.print(lastName + " " + firstName + " " + birthYear);
}
public void setKey (int k)
{
Key = k;
}
public void setOrder (int o)
{
Order = o;
}
public void setFirstName(String fName)
{
firstName = fName;
}
public void setLastName(String lName)
{
lastName = lName;
}
public void setBirthYear(String bYear)
{
birthYear = bYear;
}
}
如果相关的话,int-key应该允许我选择我想要排序的变量(名字、姓氏或出生年份),int-order应该允许我颠倒人们的排序顺序(从最小到最大,从最大到最小)
如果我不能使用comparable,这是否意味着我必须使用comparator?如果是这样,有人能告诉我怎么做吗
如果有人知道这是怎么回事,请告诉我。如果这个Main.java没有其他问题,我可以发布我的其他.java文件
我注意到的一件事是,即使我注释掉了我的选择排序函数调用,以及这个.java文件中的所有printline命令,我的屏幕上也显示了相同的输出
请让我知道你的想法,谢谢你抽出时间 你在正确的轨道上。但是,编译器如何知道您的
人类
类是可比的
?您不仅必须提供方法compareTo()
,而且必须在开始时将实现Comparable
。您的人类类似乎还可以-但是尽管您已经实现了compareTo()
函数,但您还没有声明您的类实现了Comparable
接口(这是您得到的编译错误):
谢谢,我做了您建议的更改。但是,我仍然得到相同的异常输出。我还在Main.Java中的Selection_Sort Selection=new Selection_Sort();Selection.Sort(pplArray);因为Sort()
是一个静态函数,你不需要创建一个选择排序的实例。所以只要运行Selection\u Sort.Sort(pplArray);
就足够了。除此之外,你看到了什么“不寻常的输出”?你是在谈论构建项目的输出,还是运行项目的输出?
incompatible types: Human[] cannot be converted to Comparable
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package project_1_sorting;
class Human{
String firstName;
String lastName;
String birthYear;
int Key;
int Order;
public Human() // A constructor
{
}
public int compareTo(Human person)
{
if (Order == 0)
{
if (Key == 0)
return lastName.compareTo(person.lastName );
else if (Key == 1)
return firstName.compareTo(person.firstName );
else
return birthYear.compareTo(person.birthYear );
}
else
{
if (Key == 0)
return (lastName.compareTo(person.lastName ) ) * -1;
else if (Key == 1)
return ( firstName.compareTo(person.firstName ) ) * -1;
else
return ( birthYear.compareTo(person.birthYear ) ) * -1;
}
}
public void printHuman ()
{
StdOut.print(lastName + " " + firstName + " " + birthYear);
}
public void setKey (int k)
{
Key = k;
}
public void setOrder (int o)
{
Order = o;
}
public void setFirstName(String fName)
{
firstName = fName;
}
public void setLastName(String lName)
{
lastName = lName;
}
public void setBirthYear(String bYear)
{
birthYear = bYear;
}
}
class Human implements Comparable<Human> {
@Override
public int compareTo(Human person)