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ComparatorExample.java
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153 lines (130 loc) · 4.71 KB
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package example.TmpExample;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* Comparator & Comparable 範例
* - Comparable: 可比較的，通常用在物件implements使用。
* - Comparator: 比較器，應用範圍廣，此介面提供很多默認方法供lamda expression使用
*
* ! 常被運用在排序上使用，可利用 Comparator 去為物件的屬性重新排序 (如: id, name, phone number, ..., etc)
*
* Reference:
* - https://dotblogs.com.tw/duke/2019/12/13/151221
* - https://ithelp.ithome.com.tw/articles/10229868
* - https://ithelp.ithome.com.tw/articles/10229625
* - https://www.geeksforgeeks.org/comparable-vs-comparator-in-java/
*/
public class ComparatorExample<T> {
public static void main(String[] args) {
sort();
}
public static List<Employee> generateData() {
// generate data.
List<Employee> employees = new ArrayList<>();
employees.add(new Employee(1, "George", 88888));
employees.add(new Employee(2, "May", 22222));
employees.add(new Employee(4, "Peter", 77777));
employees.add(new Employee(5, "Pany", 22256));
employees.add(new Employee(3, "John", 136241));
employees.add(new Employee(6, "HaHa", 112789));
return employees;
}
public static List<Employee> generateData2() {
// generate data.
List<Employee> employees = new ArrayList<>();
employees.add(new Employee(1, "George", 5133513));
employees.add(new Employee(2, "May", 154623));
employees.add(new Employee(4, "Peter", 214696));
employees.add(new Employee(5, "Pany", 37763546));
employees.add(new Employee(3, "John", 642425));
employees.add(new Employee(6, "HaHa", 262464688));
return employees;
}
public static void sort() {
// * sorting function.
// generate a series of employee.
List<Employee> employees = generateData();
sortingByName(employees); // sorting by name.
sortingBySalary(employees); // sorting by salary.
}
public static void sortingByName(List<Employee> employees) {
Comparator<Employee> employeeNameComparator = new Comparator<Employee>() {
@Override
public int compare(Employee e1, Employee e2) {
return e1.getName().compareTo(e2.getName());
}
};
// sorting by name.
Collections.sort(employees, employeeNameComparator);
System.out.println("===sorting by name===");
employees.forEach(s -> {
System.out.println("id: " + s.getId() + "; name: " + s.getName() + "; salary: " + s.getSalary());
});
}
public static void sortingBySalary(List<Employee> employees) {
Comparator<Employee> employeeSalayComparator = new Comparator<Employee>() {
@Override
public int compare(Employee e1, Employee e2) {
if (e1.getSalary() < e2.getSalary()) {
return -1;
} else if (e1.getSalary() > e2.getSalary()) {
return 1;
} else {
return 0;
}
}
};
// sorting by salary.
Collections.sort(employees, employeeSalayComparator);
System.out.println("===sorting by salary===");
employees.forEach(s -> {
System.out.println("id: " + s.getId() + "; name: " + s.getName() + "; salary: " + s.getSalary());
});
}
// TODO: how to use generic function and implement it.
// public void sortingByYouWant(List<T> t) {
// // TODO: think about using generic class/function to implement it.
// Comparator<T> tComparator = new Comparator<T>() {
// @Override
// public int compare(T t1, T t2) {
// // TODO: not sure how to implement it.
// return t1.getName().compareTo(t2.getName());
// }
// };
// }
}
class SortByName implements Comparator<Employee> {
// * compare Employee by name.
// TODO: add anther condition.
// https://www.geeksforgeeks.org/comparable-vs-comparator-in-java/
public int compare(Employee e1, Employee e2) {
// ! return int ??
return e1.getName().compareTo(e2.getName());
}
}
/**
* Employee's class structure.
*/
class Employee {
int id;
String name;
int salary;
Employee(int id, String name, int salary) {
this.id = id;
this.name = name;
this.salary = salary;
}
Employee() {
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public int getSalary() {
return salary;
}
}