我编写了一个代码来按名称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());
}
}
}
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()); }}
同样适用于id。 现在我想改变我的程序，就像我必须从uset获取你想要排序的基础。如果用户提供id，我必须按id排序。如果用户给出firstname，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排序，它必须按名字排序
答案 0 :(得分：1)
创建一个用户输入标记（字符串，整数等）到Comparator<Employee>的地图，并使用适当的地图。
答案 1 :(得分：0)
您的意思是想要摆脱使用switch吗？如果是这样，您可以尝试使用已注册的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。这非常复杂，如果您使用的值不是Comparable，可能会引入更多错误，例如String，Integer，Double。你必须要小心。
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());
}
}
}