public static void test1(List<String> list) {
 for (int i = 0; i < list.size(); i++) {
  System.out.println(list.get(i));
 }
}

public static void test2(List<String> list) {
 for (int i = 0,lengh=list.size(); i < lengh; i++) {
  System.out.println(list.get(i));
 }
}

public static void test3(List<String> list) {
 Iterator<String> iterator = list.iterator();
 while(iterator.hasNext()){
  System.out.println(iterator.next());
 }
}

public static void test4(List<String> list) {
 for(String str:list){
  System.out.println(str);
 }
}

public static void test5(List<String> list) {
 //list.forEach(System.out::println);和下面的写法等价
 list.forEach(str->{
  System.out.println(str);
 });
}

public static void test6(List<String> list) {
 list.iterator().forEachRemaining(str->{
  System.out.println(str);
 });
}

package test;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class Test8 {
 public static void main(String[] args) {
  List<Dog> list=new ArrayList<>();
  for(int i=0;i<10;i++){
   list.add(new Dog(i,"dog"+i));
  }
  long nanoTime = System.nanoTime();
  test1(list);
  long nanoTime1 = System.nanoTime();
  test2(list);
  long nanoTime2 = System.nanoTime();
  test3(list);
  long nanoTime3 = System.nanoTime();
  test4(list);
  long nanoTime4 = System.nanoTime();
  test5(list);
  long nanoTime5 = System.nanoTime();
  test6(list);
  long nanoTime6 = System.nanoTime();
  System.out.println((nanoTime1-nanoTime)/1000000.0);
  System.out.println((nanoTime2-nanoTime1)/1000000.0);
  System.out.println((nanoTime3-nanoTime2)/1000000.0);
  System.out.println((nanoTime4-nanoTime3)/1000000.0);
  System.out.println((nanoTime5-nanoTime4)/1000000.0);
  System.out.println((nanoTime6-nanoTime5)/1000000.0);
 }
public static void test1(List<Dog> list) {
 for (int i = 0; i < list.size(); i++) {
  list.get(i).hashCode();
 }
}
public static void test2(List<Dog> list) {
 for (int i = 0,lengh=list.size(); i < lengh; i++) {
  list.get(i).hashCode();
 }
}
public static void test3(List<Dog> list) {
 Iterator<Dog> iterator = list.iterator();
 while(iterator.hasNext()){
  iterator.next().hashCode();
 }
}
public static void test4(List<Dog> list) {
 for(Dog dog:list){
  dog.hashCode();
 }
}
public static void test5(List<Dog> list) {
 //list.forEach(System.out::println);和下面的写法等价
 list.forEach(dog->{
  dog.hashCode();
 });
}
public static void test6(List<Dog> list) {
 list.iterator().forEachRemaining(dog->{
  dog.hashCode();
 });
}
}
class Dog{
 private int age;
 private String name;
 public Dog(int age, String name) {
  super();
  this.age = age;
  this.name = name;
 }
 public int getAge() {
  return age;
 }
 public void setAge(int age) {
  this.age = age;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 @Override
 public String toString() {
  return "Dog [age=" + age + ", name=" + name + "]";
 }
}

package test;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
public class Test9 {
 public static void main(String[] args) {
  Set<Dog> set = new HashSet<>();
  for (int i = 0; i < 10_000_000; i++) {
   set.add(new Dog(i, "dog" + i));
  }
  long nanoTime = System.nanoTime();
  test1(set);
  long nanoTime1 = System.nanoTime();
  test2(set);
  long nanoTime2 = System.nanoTime();
  test3(set);
  long nanoTime3 = System.nanoTime();
  test4(set);
  long nanoTime4 = System.nanoTime();
  System.out.println((nanoTime1 - nanoTime) / 1000000.0);
  System.out.println((nanoTime2 - nanoTime1) / 1000000.0);
  System.out.println((nanoTime3 - nanoTime2) / 1000000.0);
  System.out.println((nanoTime4 - nanoTime3) / 1000000.0);
 }
 public static void test1(Set<Dog> list) {
  Iterator<Dog> iterator = list.iterator();
  while (iterator.hasNext()) {
   iterator.next().hashCode();
  }
 }
 public static void test2(Set<Dog> list) {
  for (Dog dog : list) {
   dog.hashCode();
  }
 }
 public static void test3(Set<Dog> list) {
  list.forEach(dog -> {
   dog.hashCode();
  });
 }
 public static void test4(Set<Dog> list) {
  list.iterator().forEachRemaining(dog -> {
   dog.hashCode();
  });
 }
}

package test;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class Test10 {
 public static void main(String[] args) {
  Map<String, Dog> map = new HashMap<>();
  for (int i = 0; i < 1000_000; i++) {
   map.put("dog" + i, new Dog(i, "dog" + i));
  }
  long nanoTime = System.nanoTime();
  test1(map);
  long nanoTime1 = System.nanoTime();
  test2(map);
  long nanoTime2 = System.nanoTime();
  test3(map);
  long nanoTime3 = System.nanoTime();
  test4(map);
  long nanoTime4 = System.nanoTime();
  System.out.println((nanoTime1 - nanoTime) / 1000000.0);
  System.out.println((nanoTime2 - nanoTime1) / 1000000.0);
  System.out.println((nanoTime3 - nanoTime2) / 1000000.0);
  System.out.println((nanoTime4 - nanoTime3) / 1000000.0);
 }
 public static void test1(Map<String, Dog> map) {
  Iterator<Map.Entry<String, Dog>> entries = map.entrySet().iterator();
  while (entries.hasNext()) {
   Map.Entry<String, Dog> entry = entries.next();
   int code=entry.getKey().hashCode()+entry.getValue().hashCode();
  }
 }
 public static void test2(Map<String, Dog> map) {
  for (Map.Entry<String, Dog> entry : map.entrySet()) {
   int code=entry.getKey().hashCode()+entry.getValue().hashCode();
  }
 }
 public static void test3(Map<String, Dog> map) {
  for (String key : map.keySet()) {
   int code=key.hashCode()+map.get(key).hashCode();
  }
 }
 public static void test4(Map<String, Dog> map) {
  map.forEach((key, value) -> {
   int code=key.hashCode()+value.hashCode();
  });
 }
}