Java 8 Internal Iteration: External vs. Internal Iteration
April 27, 2014
External Iteration
Suppose we have a list of employee and we need to update the salary of each and every employee multiplied by two. As old fashioned, we will do as below.ExternalIterationDemo.java
package com.concretepage.util.stream;
import java.util.List;
public class ExternalIterationDemo {
public static void main(String[] args) {
List<Employee> list = Employee.getEmpList();
for(Employee e : list){
e.setSal(e.getSal()*2);
}
}
}
Internal Iteration
Now the same task we will do in new fashion using forEach that will iterate collection internally. Find the code below.InternalIterationDemo.java
package com.concretepage.util.stream;
import java.util.List;
public class InternalIterationDemo {
public static void main(String[] args) {
List<Employee> list = Employee.getEmpList();
System.out.println("Salary before update");
list.forEach(e->System.out.print(e.getSal()+" "));
list.forEach(e->e.setSal(e.getSal()*2));
System.out.println("\nSalary after update");
list.forEach(e->System.out.print(e.getSal()+" "));
}
}
Salary before update 2000 3000 4000 5000 Salary after update 4000 6000 8000 10000The Employee class we have used is given below.
Employee.java
package com.concretepage.util.stream;
import java.util.ArrayList;
import java.util.List;
public class Employee {
public int id;
public String name;
private int sal;
public Employee(int id,String name,int sal ){
this.id = id;
this.name = name;
this.sal = sal;
}
public void setSal(int sal) {
this.sal = sal;
}
public int getSal() {
return sal;
}
public static List<Employee> getEmpList(){
List<Employee> list = new ArrayList<>();
list.add(new Employee(1, "A", 2000));
list.add(new Employee(2, "B", 3000));
list.add(new Employee(3, "C", 4000));
list.add(new Employee(4, "D", 5000));
return list;
}
}
