按ID和名字对员工详细信息进行排序的集合

Question

我已经编写了一个代码，以按ID和名字对名称进行排序。

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());
            }
        }

    }

用于按ID和名字排序我在Sort_this类中有此代码

public class EmpSortByFirstName implements Comparator<Employee>{ 
        public int compare(Employee o1, Employee o2) {  
            return o1.getFirstName().compareTo(o2.getFirstName());    }}

同样适用于ID。 现在，我想更改程序，就像我必须从用户那里获取输入时一样，您要在此基础上进行排序。 如果用户提供ID，则必须按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，则必须按ID 2进行排序，必须按名字进行排序

Answer 1

创建一个用户输入令牌（字符串，整数等）到Comparator<Employee>的映射，然后使用适当的映射。

Answer 2

您是不是想摆脱使用switch ？ 如果是这样，您可以尝试拥有已注册的Soter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());
        }
    }
}

另一个尝试通过使用反射来删除每个比较器的实现。 如果您使用的不是Comparable值，例如String ， Integer ， Double ，这将更加复杂，并且可能会引入更多错误。 您必须要小心。

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());
        }
    }
}