java lambda循环list对象 java lambda表达式循环

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mob64ca1418aeab 2024-05-15 11:37:40

文章标签 java lambda循环list对象 java lambda System Java 文章分类 Java 后端开发

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

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() {
            @Override
            public void run() {
                System.out.println("Hello world !");
            }
        }).start();

        // 1.2使用 lambda expression
        new Thread(() -> System.out.println("Hello world !")).start();

        // 2.1使用匿名内部类
        Runnable race1 = new Runnable() {
            @Override
            public void run() {
                System.out.println("Hello world !");
            }
        };

        // 2.2使用 lambda expression
        Runnable 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 players
        Arrays.sort(atp2, new Comparator<String>() {
            @Override
            public 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100
        phpProgrammers
                .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 numbers
        List<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

java lambda循环list对象 java lambda表达式循环_System

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() {
            @Override
            public void run() {
                System.out.println("Hello world !");
            }
        }).start();

        // 1.2使用 lambda expression
        new Thread(() -> System.out.println("Hello world !")).start();

        // 2.1使用匿名内部类
        Runnable race1 = new Runnable() {
            @Override
            public void run() {
                System.out.println("Hello world !");
            }
        };

        // 2.2使用 lambda expression
        Runnable 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 players
        Arrays.sort(atp2, new Comparator<String>() {
            @Override
            public 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100
        phpProgrammers
                .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 numbers
        List<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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