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Employee.java
EmployeeIdComparator.java
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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 + "]"; } }
import java.util.Comparator; public class EmployeeIdComparator implements Comparator<Employee> { /* * This method used to arrange the employee objects in descending order based * on employeeId. */ @Override public int compare( Employee employee1, Employee employee2 ) { System.out .println("\nCompare method has been called in EmployeeIdComparator,\nto arrange" + " the employee objects in descending order based on employeeId : "); System.out.println("employee1 = " + employee1 + ", employee2 = " + employee2 + "\n"); if( employee1.getEmployeeId() < employee2.getEmployeeId() ) { return 1; } else { return -1; } } }
import java.util.TreeSet; /* * Example of TreeSet(Comparator<? super E> comparator) Constructor. */ public class TreeSetExample { public static void main( String[] args ) { EmployeeIdComparator employeeIdComparator = new EmployeeIdComparator(); /* * Constructs a new, empty tree set, sorted according to the specified * comparator. * * All elements inserted into the set must be mutually comparable by the * specified comparator: comparator.compare(e1, e2) must not throw a * ClassCastException for any elements e1 and e2 in the set. * * If the user attempts to add an element to the set that violates this * constraint, the add call will throw a ClassCastException. */ TreeSet<Employee> treeSet = new TreeSet<Employee>(employeeIdComparator); Employee john = new Employee(3, "John"); Employee david = new Employee(2, "David"); Employee peter = new Employee(1, "Peter"); Employee juli = new Employee(4, "Juli"); System.out.println(john + " is going to be add in treeSet"); treeSet.add(john); System.out.println(david + " is going to be add in treeSet"); treeSet.add(david); System.out.println(peter + " is going to be add in treeSet"); treeSet.add(peter); System.out.println(juli + " is going to be add in treeSet"); treeSet.add(juli); System.out.println("treeSet : " + treeSet + "\n"); for( Employee employee : treeSet ) { System.out.println("Employee ID : "+employee.getEmployeeId()); System.out.println("Name : "+employee.getName()); System.out.println("-----------------------------------"); } } }
Employee [employeeId=3, name=John] is going to be add in treeSet Compare method has been called in EmployeeIdComparator, to arrange the employee objects in descending order based on employeeId : employee1 = Employee [employeeId=3, name=John], employee2 = Employee [employeeId=3, name=John] Employee [employeeId=2, name=David] is going to be add in treeSet Compare method has been called in EmployeeIdComparator, to arrange the employee objects in descending order based on employeeId : employee1 = Employee [employeeId=2, name=David], employee2 = Employee [employeeId=3, name=John] Employee [employeeId=1, name=Peter] is going to be add in treeSet Compare method has been called in EmployeeIdComparator, to arrange the employee objects in descending order based on employeeId : employee1 = Employee [employeeId=1, name=Peter], employee2 = Employee [employeeId=3, name=John] Compare method has been called in EmployeeIdComparator, to arrange the employee objects in descending order based on employeeId : employee1 = Employee [employeeId=1, name=Peter], employee2 = Employee [employeeId=2, name=David] Employee [employeeId=4, name=Juli] is going to be add in treeSet Compare method has been called in EmployeeIdComparator, to arrange the employee objects in descending order based on employeeId : employee1 = Employee [employeeId=4, name=Juli], employee2 = Employee [employeeId=2, name=David] Compare method has been called in EmployeeIdComparator, to arrange the employee objects in descending order based on employeeId : employee1 = Employee [employeeId=4, name=Juli], employee2 = Employee [employeeId=3, name=John] treeSet : [Employee [employeeId=4, name=Juli], Employee [employeeId=3, name=John], Employee [employeeId=2, name=David], Employee [employeeId=1, name=Peter]] Employee ID : 4 Name : Juli ----------------------------------- Employee ID : 3 Name : John ----------------------------------- Employee ID : 2 Name : David ----------------------------------- Employee ID : 1 Name : Peter -----------------------------------
https://sites.google.com/site/javaee4321/java-collections/TreeSetDemoEmployeesAscComparatorDescId.zip?attredirects=0&d=1
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