一、常用循环

public class Spring3 {public static void main(String[] args) {String[] atp = {"yuanGe","daWei","xiaoMing"};List<String> players = Arrays.asList(atp);// 以前的循环方式for (String player : players) {System.out.println(player + "; ");}System.out.println("===================================");// 使用 lambda 表达式以及函数操作(functional operation)players.forEach((player) -> System.out.println(player + "; "));System.out.println("===================================");// 在 Java 8 中使用双冒号操作符(double colon operator)players.forEach(System.out::println);}
}

二、匿名内部类

public class Spring3 {public static void main(String[] args) {// 1.1使用匿名内部类new Thread(new Runnable() {@Overridepublic void run() {System.out.println("Hello world !");}}).start();// 1.2使用 lambda expressionnew Thread(() -> System.out.println("Hello world !")).start();// 2.1使用匿名内部类Runnable race1 = new Runnable() {@Overridepublic void run() {System.out.println("Hello world !");}};// 2.2使用 lambda expressionRunnable race2 = () -> System.out.println("Hello world !");// 直接调用 run 方法(没开新线程哦!)race1.run();race2.run();}
}

三、排序集合

public class Spring3 {public static void main(String[] args) {String[] atp2 = {"Z","B","C"};// 1.1 使用匿名内部类根据 name 排序 playersArrays.sort(atp2, new Comparator<String>() {@Overridepublic int compare(String s1, String s2) {return (s1.compareTo(s2));}});List<String> players2 = Arrays.asList(atp2);players2.forEach(System.out::println);}
}

四、循环打印对象

@AllArgsConstructor//创建带参构造器
@Data//get、set方法，为该类添加equals、canEquals、hashCode、toString方法
@Slf4j//log的Log4J日志对象
public class Person {@NonNull//属性非空private String a;private String b;private String c;private String d;private Integer e;private Integer f;
}public class Spring3 {public static void main(String[] args) {List<Person> javaProgrammers = new ArrayList<Person>() {{add(new Person("Elsdon", "Jaycob", "Java programmer", "male", 43, 2000));add(new Person("Tamsen", "Brittany", "Java programmer", "female", 23, 1500));add(new Person("Floyd", "Donny", "Java programmer", "male", 33, 1800));add(new Person("Sindy", "Jonie", "Java programmer", "female", 32, 1600));add(new Person("Vere", "Hervey", "Java programmer", "male", 22, 1200));add(new Person("Maude", "Jaimie", "Java programmer", "female", 27, 1900));add(new Person("Shawn", "Randall", "Java programmer", "male", 30, 2300));add(new Person("Jayden", "Corrina", "Java programmer", "female", 35, 1700));add(new Person("Palmer", "Dene", "Java programmer", "male", 33, 2000));add(new Person("Addison", "Pam", "Java programmer", "female", 34, 1300));}};List<Person> phpProgrammers = new ArrayList<Person>() {{add(new Person("Jarrod", "Pace", "PHP programmer", "male", 34, 1550));add(new Person("Clarette", "Cicely", "PHP programmer", "female", 23, 1200));add(new Person("Victor", "Channing", "PHP programmer", "male", 32, 1600));add(new Person("Tori", "Sheryl", "PHP programmer", "female", 21, 1000));add(new Person("Osborne", "Shad", "PHP programmer", "male", 32, 1100));add(new Person("Rosalind", "Layla", "PHP programmer", "female", 25, 1300));add(new Person("Fraser", "Hewie", "PHP programmer", "male", 36, 1100));add(new Person("Quinn", "Tamara", "PHP programmer", "female", 21, 1000));add(new Person("Alvin", "Lance", "PHP programmer", "male", 38, 1600));add(new Person("Evonne", "Shari", "PHP programmer", "female", 40, 1800));}};javaProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getA(), p.getB()));phpProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getA(), p.getB()));}
}

总结

for(Object o: list) { // 外部迭代System.out.println(o);}
//可以写成：
list.forEach(o -> {System.out.println(o);}); //forEach函数实现内部迭代

五、根据条件修改

filter方法的参数是Predicate类型，forEach方法的参数是Consumer类型，它们都是函数式接口，所以可以使用λ表达式。
将E属性为34的对象将其F属性设置为100

public class Spring3 {public static void main(String[] args) {//将E属性为34的对象将其F属性设置为100phpProgrammers.stream().filter(s -> s.getE() == 34).forEach(s -> s.setF(100));phpProgrammers.forEach(o -> System.out.println(o.toString()));}
}

六、排序

public class Spring3 {public static void main(String[] args) {//根据A列名字排序List<Person> sortedJavaProgrammers = javaProgrammers.stream().sorted((p, p2) -> (p.getA().compareTo(p2.getA()))).limit(5).collect(Collectors.toList());sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getA(), p.getB()));//根据F列数字排序sortedJavaProgrammers = javaProgrammers.stream().sorted((p, p2) -> (p.getF() - p2.getF())).collect(Collectors.toList());sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getA(), p.getB()));}
}

七、求和

上面的例子中我们已经看到 collect 方法是如何工作的。结合 map 方法,我们可以使用 collect 方法来将我们的结果集放到一个字符串,一个 Set 或一个TreeSet中:

public class Spring3 {public static void main(String[] args) {int totalSalary = javaProgrammers.parallelStream().mapToInt(p -> p.getF()).sum();System.out.println(totalSalary);}
}

八、统计方法

public class Spring3 {public static void main(String[] args) {//计算 count, min, max, sum, and average for numbersList<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);IntSummaryStatistics stats = numbers.stream().mapToInt((x) -> x).summaryStatistics();System.out.println("List中最大的数字 : " + stats.getMax());System.out.println("List中最小的数字 : " + stats.getMin());System.out.println("所有数字的总和   : " + stats.getSum());System.out.println("所有数字的平均值 : " + stats.getAverage());}
}

九、材料

本文一共两个用到两个类

import lombok.*;
import lombok.extern.java.Log;
import lombok.extern.log4j.Log4j;
import lombok.extern.slf4j.Slf4j;/*** @author lichangyuan* @create 2021-09-27 16:34*/
@AllArgsConstructor//创建带参构造器
@Data//get、set方法，为该类添加equals、canEquals、hashCode、toString方法
@Slf4j//log的Log4J日志对象
@Log
public class Person {@NonNull//属性非空private String a;private String b;private String c;private String d;private Integer e;private Integer f;
}

import com.example.demo.entity.Person;import java.util.*;
import java.util.stream.Collectors;/*** @author lichangyuan* @create 2021-09-26 16:44*/
public class Spring3 {public static void main(String[] args) {String[] atp = {"yuanGe","daWei","xiaoMing"};List<String> players = Arrays.asList(atp);// 以前的循环方式for (String player : players) {System.out.println(player + "; ");}System.out.println("===================================");// 使用 lambda 表达式以及函数操作(functional operation)players.forEach((player) -> System.out.println(player + "; "));System.out.println("===================================");// 在 Java 8 中使用双冒号操作符(double colon operator)players.forEach(System.out::println);System.out.println("===================================");// 1.1使用匿名内部类new Thread(new Runnable() {@Overridepublic void run() {System.out.println("Hello world !");}}).start();// 1.2使用 lambda expressionnew Thread(() -> System.out.println("Hello world !")).start();// 2.1使用匿名内部类Runnable race1 = new Runnable() {@Overridepublic void run() {System.out.println("Hello world !");}};// 2.2使用 lambda expressionRunnable race2 = () -> System.out.println("Hello world !");// 直接调用 run 方法(没开新线程哦!)race1.run();race2.run();System.out.println("===================================");String[] atp2 = {"Z", "B", "C"};// 1.1 使用匿名内部类根据 name 排序 playersArrays.sort(atp2, new Comparator<String>() {@Overridepublic int compare(String s1, String s2) {return (s1.compareTo(s2));}});List<String> players2 = Arrays.asList(atp2);players2.forEach(System.out::println);System.out.println("===================================");List<Person> javaProgrammers = new ArrayList<Person>() {{add(new Person("Elsdon", "Jaycob", "Java programmer", "male", 43, 2000));add(new Person("Tamsen", "Brittany", "Java programmer", "female", 23, 1500));add(new Person("Floyd", "Donny", "Java programmer", "male", 33, 1800));add(new Person("Sindy", "Jonie", "Java programmer", "female", 32, 1600));add(new Person("Vere", "Hervey", "Java programmer", "male", 22, 1200));add(new Person("Maude", "Jaimie", "Java programmer", "female", 27, 1900));add(new Person("Shawn", "Randall", "Java programmer", "male", 30, 2300));add(new Person("Jayden", "Corrina", "Java programmer", "female", 35, 1700));add(new Person("Palmer", "Dene", "Java programmer", "male", 33, 2000));add(new Person("Addison", "Pam", "Java programmer", "female", 34, 1300));}};List<Person> phpProgrammers = new ArrayList<Person>() {{add(new Person("Jarrod", "Pace", "PHP programmer", "male", 34, 1550));add(new Person("Clarette", "Cicely", "PHP programmer", "female", 23, 1200));add(new Person("Victor", "Channing", "PHP programmer", "male", 32, 1600));add(new Person("Tori", "Sheryl", "PHP programmer", "female", 21, 1000));add(new Person("Osborne", "Shad", "PHP programmer", "male", 32, 1100));add(new Person("Rosalind", "Layla", "PHP programmer", "female", 25, 1300));add(new Person("Fraser", "Hewie", "PHP programmer", "male", 36, 1100));add(new Person("Quinn", "Tamara", "PHP programmer", "female", 21, 1000));add(new Person("Alvin", "Lance", "PHP programmer", "male", 38, 1600));add(new Person("Evonne", "Shari", "PHP programmer", "female", 40, 1800));}};javaProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getA(), p.getB()));phpProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getA(), p.getB()));System.out.println("===================================");//根据A列名字排序List<Person> sortedJavaProgrammers = javaProgrammers.stream().sorted((p, p2) -> (p.getA().compareTo(p2.getA()))).limit(5).collect(Collectors.toList());sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getA(), p.getB()));//根据F列数字排序sortedJavaProgrammers = javaProgrammers.stream().sorted((p, p2) -> (p.getF() - p2.getF())).collect(Collectors.toList());sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getA(), p.getB()));System.out.println("===================================");//将E属性为34的对象将其F属性设置为100phpProgrammers.stream().filter(s -> s.getE() == 34).forEach(s -> s.setF(100));phpProgrammers.forEach(o -> System.out.println(o.toString()));System.out.println("===================================");int totalSalary = javaProgrammers.parallelStream().mapToInt(p -> p.getF()).sum();System.out.println(totalSalary);System.out.println("===================================");//计算 count, min, max, sum, and average for numbersList<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);IntSummaryStatistics stats = numbers.stream().mapToInt((x) -> x).summaryStatistics();System.out.println("List中最大的数字 : " + stats.getMax());System.out.println("List中最小的数字 : " + stats.getMin());System.out.println("所有数字的总和   : " + stats.getSum());System.out.println("所有数字的平均值 : " + stats.getAverage());}
}

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Java 8 新特性Lambda 表达式

Java 8 新特性Lambda 表达式

一、常用循环

二、匿名内部类

三、排序集合

四、循环打印对象

五、根据条件修改

六、排序

七、求和

八、统计方法

九、材料

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