JAVA EE: Java : Collection Framework : Collections (Max Comparator)

Friday, 10 July 2015

Java : Collection Framework : Collections (Max Comparator)

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Java : Collection Framework : Collections (Max Comparator)

Employee.java

public class Employee

{
    private int    employeeId;
    private String name;

    public Employee( int employeeId, String name )
    {
        super();
        this.employeeId = employeeId;
        this.name = name;
    }

    public int getEmployeeId()
    {
        return employeeId;
    }

    public void setEmployeeId( int employeeId )
    {
        this.employeeId = employeeId;
    }

    public String getName()
    {
        return name;
    }

    public void setName( String name )
    {
        this.name = name;
    }

    @Override
    public String toString()
    {
        return "Employee [employeeId=" + employeeId + ", name=" + name + "]";
    }

}

EmployeeIdComparator.java

import java.util.Comparator;

public class EmployeeIdComparator implements Comparator<Employee>
{

    /*
     * This method used to order the employee objects in Ascending based on employeeId.
     */
    @Override
    public int compare(Employee employee1, Employee employee2)
    {

        if (employee1.getEmployeeId() < employee2.getEmployeeId())
        {
            return -1;
        }
        else
        {
            return 1;
        }

    }

}

CollectionsExample.java

import java.util.ArrayList;
import java.util.Collections;

/*
 Method: 

 public static <T> T max(Collection<? extends T> coll,
                                    Comparator<? super T> comp)

 Parameters:

 coll - the collection whose maximum element is to be determined.
 comp - the comparator with which to determine the maximum element. 
        A null value indicates that the elements' natural ordering 
        should be used.

 Returns:

 the maximum element of the given collection, according to the 
 specified comparator.

 */

public class CollectionsExample
{

    public static void main(String[] args)
    {

        ArrayList<Employee> employeeList = new ArrayList<Employee>();

        Employee john = new Employee(3, "John");
        Employee david = new Employee(2, "David");
        Employee peter = new Employee(1, "Peter");
        Employee juli = new Employee(5, "Juli");
        Employee ram = new Employee(4, "Ram");

        employeeList.add(john);
        employeeList.add(david);
        employeeList.add(peter);
        employeeList.add(juli);
        employeeList.add(ram);

        System.out.println("employeeList : " + employeeList + "\n");

        EmployeeIdComparator employeeIdComparator = new EmployeeIdComparator();
        
        /*
         * Returns the maximum element of the given collection, according to the
         * order induced by the specified comparator.
         */
        Employee employee = Collections.max(employeeList,
                employeeIdComparator);

        System.out.println("employee object whose employee id is max : " + employee);
        
    }
}

Output

employeeList : [Employee [employeeId=3, name=John], Employee [employeeId=2, name=David], 
Employee [employeeId=1, name=Peter], Employee [employeeId=5, name=Juli], 
Employee [employeeId=4, name=Ram]]

employee object whose employee id is max : Employee [employeeId=5, name=Juli]