package test;
import java.util.ArrayList;
import java.util.List;
public class StreamTest {
 static List < Integer > myList = new ArrayList < > ();
 public static void main(String[] args) {
 for (int i = 0; i < 5000000; i++)
 myList.add(i);
 int result = 0;
 long loopStartTime = System.currentTimeMillis();
 for (int i: myList) {
 if (i % 2 == 0)
 result += i;
 }
 long loopEndTime = System.currentTimeMillis();
 System.out.println(result);
 System.out.println("Loop total Time = " + (loopEndTime - loopStartTime));
 long streamStartTime = System.currentTimeMillis();
 System.out.println(myList.stream().filter(value -> value % 2 == 0).mapToInt(Integer::intValue).sum());
 long streamEndTime = System.currentTimeMillis();
 System.out.println("Stream total Time = " + (streamEndTime - streamStartTime));
 long parallelStreamStartTime = System.currentTimeMillis();
 System.out.println(myList.parallelStream().filter(value -> value % 2 == 0).mapToInt(Integer::intValue).sum());
 long parallelStreamEndTime = System.currentTimeMillis();
 System.out.println("Parallel Stream total Time = " + (parallelStreamEndTime - parallelStreamStartTime));
 }
}

820084320
Loop total Time = 17
820084320
Stream total Time = 81
820084320
Parallel Stream total Time = 30

package test;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class StreamLazinessTest {
 /** Employee class **/
 static class Employee {
 int id;
 String name;
 public Employee(int id, String name) {
 this.id = id;
 this.name = name;
 }
 public String getName() {
 return this.name;
 }
 }
 public static void main(String[] args) throws InterruptedException {
 List < Employee > employees = new ArrayList < > ();
 /** Creating the employee list **/
 for (int i = 1; i < 10000000; i++) {
 employees.add(new StreamLazinessTest.Employee(i, "name_" + i));
 }
 /** Only Intermediate Operations; it will just create another streams and 
 * will not perform any operations **/
 Stream < String > employeeNameStreams = employees.parallelStream().filter(employee -> employee.id % 2 == 0)
 .map(employee -> {
 System.out.println("In Map - " + employee.getName());
 return employee.getName();
 });
 /** Adding some delay to make sure nothing has happen till now **/
 Thread.sleep(2000);
 System.out.println("2 sec");
 /** Terminal operation on the stream and it will invoke the Intermediate Operations
 * filter and map **/
 employeeNameStreams.collect(Collectors.toList());
 }
}

StreamShortCircuitTest.java:
package test;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class StreamShortCircuitTest {
 /** Employee class **/
 static class Employee {
 int id;
 String name;
 public Employee(int id, String name) {
 this.id = id;
 this.name = name;
 }
 public int getId() {
 return this.id;
 }
 public String getName() {
 return this.name;
 }
 }
 public static void main(String[] args) throws InterruptedException {
 List < Employee > employees = new ArrayList < > ();
 for (int i = 1; i < 10000000; i++) {
 employees.add(new StreamShortCircuitTest.Employee(i, "name_" + i));
 }
 /** Only Intermediate Operations; it will just create another streams and 
 * will not perform any operations **/
 Stream < String > employeeNameStreams = employees.stream().filter(e -> e.getId() % 2 == 0)
 .map(employee -> {
 System.out.println("In Map - " + employee.getName());
 return employee.getName();
 });
 long streamStartTime = System.currentTimeMillis();
 /** Terminal operation with short-circuit operation: limit **/
 employeeNameStreams.limit(100).collect(Collectors.toList());
 System.out.println(System.currentTimeMillis() - streamStartTime);
 }
}