无法按字母顺序对数组列表进行排序
[英]Having trouble sorting array list alphabetically
问题描述
我一直无法将sort my outputs into alphabetical order （按名称） sort my outputs into alphabetical order 。 我尝试了几种methods ，但已将其注释掉。 我尝试过的最新方法是bubble sort 。
我的程序将所有输入写入二进制文件，然后在用户想要输出它们时读取它们。 因此，基本上，当用户单击数字5时，它将run sortEmployees()方法，然后以字母顺序显示记录，但是目前我还没有找到一种方法。
我对数组列表不确定，我没有使用太多...所以我几乎可以肯定我使用了错误的methods 。 我没有使用最新的JDK。 我也在堆栈+ google上查看了不同的问题，但实际上找不到很多帮助。
目前的输出如下：
- 1，约翰逊，80000.00
- 2等等...
- 3，依此类推...如下所述。
我将在下面添加所有代码，因此您可以看一下。
EmployeeFileDriver.java
java.io.*;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import javax.swing.JOptionPane;
public class EmployeeFileDriver
{
private static ArrayList<Employee> list = new ArrayList<>();
public static void main(String args[]) throws IOException
{
final int QUIT_MAIN_MENU = 4;
String fileName = "Employee.txt";
readEmployeeFile(fileName);
//sample records
list.add(new Employee(1, "Johnson", 80000.00));
list.add(new Employee(2, "Singh", 75000.00));
list.add(new Employee(3, "Smith", 63000.00));
list.add(new Employee(4, "Jones", 52000.00));
int choice = mainMenu();
while(choice != QUIT_MAIN_MENU)
{
switch (choice)
{
case 1:
list.add(inputEmployee());
break;
case 2:
searchID();
break;
case 3:
listAllEmployees();
break;
case 5:
sortEmployees(list[]);
break;
} //end switch (choice)
choice = mainMenu(); // recall mainMenu()
} // end while
saveEmployeeFile(fileName); //save objects to file before closing
System.out.println("Records saved to file");
}
public static int mainMenu()
{
String heading, menu, userSelection;
heading = "<h3><u>EMPLOYEE SYSTEM</u></h3>";
menu = "<HTML><center>" + heading + "<hr><h2><u>Main Menu</u></h2><br /><table>" +
"<tr><td>1. Enter Employee Details</td></tr>" +
"<tr><td>2. Search Employee ID</td></tr>" +
"<tr><td>3. List all Employees</td></tr>" +
"<tr><td>4. Save and Exit</td></tr>" +
"<tr><td>5. Sort alphabetically</td></tr>" +
"</table><br /><hr></center></HTML>" +
"\nEnter Selection: ";
//get user selection for main menu
userSelection = JOptionPane.showInputDialog(null , menu,"Input",
JOptionPane.PLAIN_MESSAGE);
int option = Integer.parseInt(userSelection);
//return option to main method
return option;
}
public static void readEmployeeFile(String fileName)
{
try
{
//open InputFile
FileInputStream fiStream = new FileInputStream(fileName);
ObjectInputStream inStream = new ObjectInputStream(fiStream);
list = (ArrayList)inStream.readObject(); //read whole ArrayList object
//rather than individual Employee objects
System.out.println("\tEMPLOYEE LIST (from File)");
System.out.println("ID \t Name \t Salary\n");
for(Employee e: list)
{
System.out.printf("%-10d %-16s $%8.2f\n", e.getID(),
e.getName(), e.getSalary());
}
inStream.close();
}
catch (FileNotFoundException e)
{
System.err.println("Could not open file\n" + e.toString());
}
catch (ClassNotFoundException e)
{
System.err.println("Class not found \n" + e.toString());
}
catch (IOException e)
{
System.err.println("Employee file: \n" + e.toString());
}
}
//save employee objects to file on exit
public static void saveEmployeeFile(String fileName)
{
try
{
//open OutputFile
FileOutputStream foStream = new FileOutputStream(fileName);
//FileWriter fw = new FileWriter(fileName);
ObjectOutputStream outStream = new ObjectOutputStream(foStream);
outStream.writeObject(list); //save whole ArrayList object to file
outStream.close();
}
catch (FileNotFoundException e)
{
System.out.println("Could not open file\n" + e.toString());
}
catch(IOException e)
{
System.out.println("I/O error\n" + e.toString());
}
}
public static Employee inputEmployee()
{
int id;
String name;
double salary;
Employee emp;
id = Integer.parseInt(
JOptionPane.showInputDialog(null , "Enter employee ID"));
name = JOptionPane.showInputDialog(null , "Enter employee name");
salary = Double.parseDouble(
JOptionPane.showInputDialog(null , "Enter employee salary"));
emp = new Employee(id, name, salary);
return emp;
}
public static void searchID()
{
int id;
boolean found = false;
id = Integer.parseInt(
JOptionPane.showInputDialog(null, "Enter employee ID to search"));
for(Employee e: list)
{
if(id == e.getID())
{
JOptionPane.showMessageDialog(null, e.toString());
found = true;
}
}
if(found == false)
JOptionPane.showMessageDialog(null, "Employee ID not found");
}
public static void listAllEmployees()
{
String output = "";
for(Employee e: list)
{
output += e.toString();
}
JOptionPane.showMessageDialog(null, output);
}
// public void sortEmployees(){
// //Collections.sort(list, (e1, e2) -> e1.getname().compareTo(e2.id()));
// //[list sortUsingSelector:@selector(caseInsensitiveCompare:)];
// Collections.sort(list, new Comparator<Employee>()
// {
// @Override
// public int compare(String name)
// {
// return name.compareToIgnoreCase("ABCDE");
// }
// });
// }
public static void sortEmployees()
{
int j;
boolean flag = true; // will determine when the sort is finished
String temp;
while ( flag )
{
flag = false;
for ( j = 0; j < list.length - 1; j++ )
{
if ( list [ j ].compareToIgnoreCase( list [ j+1 ] ) > 0 )
{ // ascending sort
temp = list [ j ];
list [ j ] = list [ j+1]; // swapping
list [ j+1] = temp;
flag = true;
}
}
}
String output = "";
for(String e: list)
{
output += e.toString();
}
JOptionPane.showMessageDialog(null, output);
}
}
Employee.java
public class Employee
{
private int id;
private String name;
private double salary;
public Employee (int id, String name, double salary)
{
this.id = id;
this.name = name;
this.salary = salary;
}
public void setName(String name)
{
this.name = name;
}
public String getName()
{
return this.name;
}
public double getSalary()
{
return this.salary;
}
public int getID()
{
return this.id;
}
public String toString()
{
return "\nID_NO:\t"+id+"\nNAME:\t"+name+"\nSALARY\t"+salary+"\n";
}
}
2 个解决方案
解决方案1
1 已采纳 2015-03-26 09:31:25
这应该做的工作。
static List<Employee> list = new ArrayList<>();
static void sortEmployees() {
list.sort(new Comparator<Employee>() {
@Override
public int compare(Employee e1, Employee e2) {
return e1.getName().compareTo(e2.getName());
}});
}
注意list.sort(...)从Java 8开始可用。对于Java 7及之前使用， Collections.sort(list, new Comparator<Employee>() {...});
对于java8流，如果要保留原始顺序：
List<Employee> sortedList = list.stream()
.sorted((e1, e2) -> e1.getName().compareTo(e2.getName()))
.collect(Collectors.toList());
另一个变体是让Employee实现Comparable接口并在Employee对象上使用自然顺序（定义时-名称上的字母顺序）：
public class Employee implements Comparable {
@Override
public int compareTo(Object o) {
Employee e = (Employee)o;
return name.compareTo(e.getName());
}
// ...
}
然后，您可以这样做（Java 8）：
static void sortEmployees() {
list.sort(null); // passing a null Comparator => use natural order
}
或在Java 7及更低版本中：
static void sortEmployees() {
Collections.sort(list);
}
解决方案2
0 2015-03-26 09:28:07
如果要按名称对所有对象排序，则需要使用Comparator或Camparable接口。
public class Employee implements Comparable<Employee>{
}
另外，您还需要重写compareto方法。
@Override
public int compare(Employee o1, Employee o2) {
return o1.name.compareTo(o2.name);
}
检查以下链接以获取更多详细信息。
http://javarevisited.blogspot.in/2014/01/java-comparator-example-for-custom.html
http://www.tutorialspoint.com/java/java_using_comparator.htm
希望对您有帮助！！
数组列表排序困难
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