Java 用于按 ID 和名字对员工详细信息进行排序的集合
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collections for sorting employee details by id & firstname
提问by Sumithra
I have written a code to sort name by id and firstname.
我写了一个代码来按 id 和名字对 name 进行排序。
import java.io.*;
import java.util.*;
public class TestEmployeeSort {
/**
* @param args
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
String option=null;
System.out.println("Enter on which order sorting should be done \n1.Id \n2.FirstName \n3.LastName");
List<Employee> coll = Name_Insert.getEmployees();
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
option=br.readLine();
int a=Integer.parseInt(option);
switch(a)
{
case 1:
Collections.sort(coll);
printList(coll);
break;
case 2:
Collections.sort(coll,new EmpSortByFirstName());// sort method
printList(coll);
break;
case 3:
Collections.sort(coll,new SortByLastName());// sort method
printList(coll);
}
}
private static void printList(List<Employee> list) {
System.out.println("EmpId\tFirstName\tLastName\tDate Of Joining\tDate of Birth");
for (int i=0;i<list.size();i++) {
Employee e=list.get(i);
System.out.println(e.getEmpId() + "\t" + e.getFirstName() + "\t" + e.getLastname() +"\t" + e.getDate_Of_Joining()+"\t"+e.getDate_Of_Birth());
}
}
}
for sorting by id and first name i have this code in the Sort_this class
为了按 id 和名字排序，我在 Sort_this 类中有这个代码
public class EmpSortByFirstName implements Comparator<Employee>{
public int compare(Employee o1, Employee o2) {
return o1.getFirstName().compareTo(o2.getFirstName()); }}
similarly for id. Now i want to change my program like i have to get input from uset on which basis you want to sort. If the user gives id, I have to sort by id. If the user gives firstname then sort by first name. I want to use if statement. If user enters 1 it has to sort by id 2 it has to sort by first name
id 也一样。现在我想改变我的程序，就像我必须从你想要排序的基础上从 uset 获取输入一样。如果用户提供id，我必须按id排序。如果用户提供名字，则按名字排序。我想使用 if 语句。如果用户输入 1 它必须按 id 2 排序它必须按名字排序
回答by Ignacio Vazquez-Abrams
Create a map of user input tokens (string, integer, etc.) to Comparator<Employee>, and just use the appropriate one.
创建用户输入标记（字符串、整数等）到 的映射Comparator<Employee>，然后使用适当的标记。
回答by gigadot
Did you mean you want to get rid of using switch? If so, you can try having a map of registered soter:
你的意思是你想摆脱使用switch？如果是这样，您可以尝试使用注册 soter 的地图：
import java.io.*;
import java.util.*;
public class TestEmployeeSort {
private static class EmployeeSortingManager {
private final List list;
private final Map<Integer, Comparator> registeredSorter = new HashMap<Integer, Comparator>();
public EmployeeSortingManager(List list) {
this.list = list;
registerAvailableSorters();
}
private void registerAvailableSorters() {
registeredSorter.put(1, null);
registeredSorter.put(2, new EmpSortByFirstName());
registeredSorter.put(3, new SortByLastName());
}
public void sortBy(int i) {
Comparator comparator = registeredSorter.get(i);
if (registeredSorter.get(i) != null) {
Collections.sort(list, comparator);
} else {
Collections.sort(list);
}
}
}
/**
* @param args
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
String option = null;
System.out.println("Enter on which order sorting should be done \n1.Id \n2.FirstName \n3.LastName");
List<Employee> coll = Name_Insert.getEmployees();
EmployeeSortingManager employeeSortingManager = new EmployeeSortingManager(coll);
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
option = br.readLine();
int a = Integer.parseInt(option);
employeeSortingManager.sortBy(a);
printList(coll);
}
private static void printList(List<Employee> list) {
System.out.println("EmpId\tFirstName\tLastName\tDate Of Joining\tDate of Birth");
for (int i = 0; i < list.size(); i++) {
Employee e = list.get(i);
System.out.println(e.getEmpId() + "\t" + e.getFirstName() + "\t" + e.getLastname() + "\t" + e.getDate_Of_Joining() + "\t" + e.getDate_Of_Birth());
}
}
}
Another attemp to remove implementation of Every single comparator through the use of reflection. This is mmore complicated and may introduced more error if you are working with values which are not Comparable, e.g. String, Integer, Double. You will have to be careful.
另一种尝试通过使用反射来删除 Every single compare 的实现。这更复杂，如果您使用的值不是Comparable，例如String，Integer，可能会引入更多错误Double。你必须小心。
import java.io.*;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.*;
public class TestEmployeeSort {
private static class EmployeeSortingManager {
private final List list;
private final Map<Integer, Method> registeredSorter = new HashMap();
private BasicComparator comparator = new BasicComparator();
public EmployeeSortingManager(List list) {
this.list = list;
registerAvailableSorters();
}
private void registerAvailableSorters() {
registeredSorter.put(1, null);
registeredSorter.put(2, getEmployeeGetMethod("firstName"));
registeredSorter.put(3, getEmployeeGetMethod("lastName"));
}
private Method getEmployeeGetMethod(String fieldName) {
Method method = null;
try {
// create java style get method name from field name, e.g. getFieldName from fieldName
String getMethodName = "get" + fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);
method = Employee.class.getMethod(getMethodName);
} catch (NoSuchMethodException ex) {
} catch (SecurityException ex) {
}
// null is return if you give invalid field name
return method;
}
public void sortBy(int i) {
Method get = registeredSorter.get(i);
if (get != null) {
comparator.setGetMethod(get);
Collections.sort(list, comparator);
} else {
Collections.sort(list);
}
}
}
private static class BasicComparator implements Comparator<Employee> {
private Method aGetMethod = null;
public void setGetMethod(Method aGetMethod) {
this.aGetMethod = aGetMethod;
}
@Override
public int compare(Employee o1, Employee o2) {
try {
Object value1 = aGetMethod.invoke(o1);
Object value2 = aGetMethod.invoke(o2);
if (value1 instanceof Comparable && value2 instanceof Comparable) {
// this should work with String, Integer, Double, etc. They all implement Comparable interface.
return ((Comparable) value1).compareTo((Comparable) value2);
} else {
// you will need to add your own comparision for other type of variable;
// obviously it is not possible to have a single comparison
// if your get method return something else.
}
} catch (IllegalAccessException ex) {
} catch (IllegalArgumentException ex) {
} catch (InvocationTargetException ex) {
}
// if cannot compare then they are equal.
return 0;
}
}
/**
* @param args
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
String option = null;
System.out.println("Enter on which order sorting should be done \n1.Id \n2.FirstName \n3.LastName");
List<Employee> coll = Name_Insert.getEmployees();
EmployeeSortingManager employeeSortingManager = new EmployeeSortingManager(coll);
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
option = br.readLine();
int a = Integer.parseInt(option);
employeeSortingManager.sortBy(a);
printList(coll);
}
private static void printList(List<Employee> list) {
System.out.println("EmpId\tFirstName\tLastName\tDate Of Joining\tDate of Birth");
for (int i = 0; i < list.size(); i++) {
Employee e = list.get(i);
System.out.println(e.getEmpId() + "\t" + e.getFirstName() + "\t" + e.getLastname() + "\t" + e.getDate_Of_Joining() + "\t" + e.getDate_Of_Birth());
}
}
}
