Prerrequisitos: Colecciones de Java, Lista de arreglos de Java, Interfaz de comparación en Java
Dado un objeto de lista que contiene varios registros, nuestra tarea es realizar un grupo SQL en los campos de la lista en Java.
Input: A list containing employee records
in random order.
Output: List sorted first by department
and then by age in each department
Acercarse:
- Ordene la lista usando el comparador por departamento y edad respectivamente.
- Luego usamos primero el método collections.sort() para la clasificación.
- Ordenaremos la lista usando el método thenComparing() de Comparator Interface. Usar este método es muy fácil y se puede usar para enstringr múltiples comparadores, lo que facilita el proceso.
A continuación se muestra la implementación del enfoque anterior:
Programa:
// Java code to implement SQL GROUP BY
import java.util.*;
// Create the employee class
class Employee {
int empid;
String name;
int age;
String dept;
int salary;
public Employee(int empid, String name, int age,
String dept, int sal)
{
this.name = name;
this.empid = empid;
this.age = age;
this.dept = dept;
this.salary = sal;
}
public String getDept()
{
return this.dept;
}
public static void main(String[] args)
{
// create the employee list
List<Employee> empData
= new ArrayList<Employee>();
// add values to list by
// using the add() method
// of the list interface
empData.add(new Employee(1, "Ajay",
25, "Technical", 35000));
empData.add(new Employee(3, "Chandan",
22, "Technical", 30000));
empData.add(new Employee(4, "Arjun",
30, "Management", 54000));
empData.add(new Employee(2, "Arun",
28, "Sales", 9000));
empData.add(new Employee(8, "Anmol",
40, "Sales", 15000));
empData.add(new Employee(9, "Vivek",
20, "Management", 8000));
empData.add(new Employee(10, "Nikhil",
27, "Sales", 7000));
empData.add(new Employee(5, "Rahul",
45, "Management", 60000));
empData.add(new Employee(6, "Ganesh",
32, "Sales", 35000));
empData.add(new Employee(7, "Vishal",
35, "Technical", 40000));
empData.add(new Employee(11, "Anmol",
23, "Sales", 15000));
empData.add(new Employee(12, "Vivek",
29, "Management", 8000));
empData.add(new Employee(13, "Nikhil",
30, "Technical", 7000));
System.out.println("\n Employee list"
+ " before sorting...\n");
System.out.println(" ID Name Age"
+ " Department Salary \n");
for (Employee e : empData) {
System.out.format(" %2d %7s %d %10s %d \n",
e.empid, e.name, e.age, e.dept, e.salary);
}
// Sorting the list by department
// and age by using the thenComparing() method
Collections.sort(empData,
new DepartmentComparator()
.thenComparing(new AgeComparator()));
System.out.println("\n Employee list after sorting...\n");
System.out.println(" ID Name Age Department Salary \n");
for (Employee emp : empData) {
System.out.format(" %2d %7s %d %10s %d \n",
emp.empid, emp.name, emp.age,
emp.dept, emp.salary);
}
}
}
class DepartmentComparator implements Comparator<Employee> {
public int compare(Employee e1, Employee e2)
{
return e1.dept.compareTo(e2.dept);
}
}
class AgeComparator implements Comparator<Employee> {
public int compare(Employee e1, Employee e2)
{
if (e1.age == e2.age)
return 0;
else if (e1.age > e2.age)
return 1;
else
return -1;
}
}
Producción:
Employee list before sorting... ID Name Age Department Salary 1 Ajay 25 Technical 35000 3 Chandan 22 Technical 30000 4 Arjun 30 Management 54000 2 Arun 28 Sales 9000 8 Anmol 40 Sales 15000 9 Vivek 20 Management 8000 10 Nikhil 27 Sales 7000 5 Rahul 45 Management 60000 6 Ganesh 32 Sales 35000 7 Vishal 35 Technical 40000 11 Anmol 23 Sales 15000 12 Vivek 29 Management 8000 13 Nikhil 30 Technical 7000 Employee list after sorting... ID Name Age Department Salary 9 Vivek 20 Management 8000 12 Vivek 29 Management 8000 4 Arjun 30 Management 54000 5 Rahul 45 Management 60000 11 Anmol 23 Sales 15000 10 Nikhil 27 Sales 7000 2 Arun 28 Sales 9000 6 Ganesh 32 Sales 35000 8 Anmol 40 Sales 15000 3 Chandan 22 Technical 30000 1 Ajay 25 Technical 35000 13 Nikhil 30 Technical 7000 7 Vishal 35 Technical 40000
Nota: En el resultado anterior, la lista está agrupada por departamentos y los departamentos están ordenados por edad de los empleados.
Publicación traducida automáticamente
Artículo escrito por vipinbailwal_gfg2018 y traducido por Barcelona Geeks. The original can be accessed here. Licence: CCBY-SA