【Java系列】JDK 1.8 新特性之 Lambda表达式

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1、Lambda表达式介绍

Lambda是一个匿名函数，我们可以将Lambda表达式理解为一段可以传递的代码（将代码像数据一样传递）。使用它可以写出简洁、灵活的代码。作为一种更紧凑的代码风格，使java语言表达能力得到提升。

2、从匿名类到Lambda转换

package com.chen.test.JAVA8Features;
​
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
​
public class Demo01 {
    private static Logger log = LoggerFactory.getLogger(Demo01.class);
​
    public static void main(String[] args) {
        Runnable t1 =new Runnable(){
            @Override
            public void run(){
                log.info("我是没有使用Lambda表达式：不简洁");
            }
        };
        
        Runnable t2 = () -> log.info("我是使用Lambda表达式：简洁、灵活");
        
        t1.run();
        t2.run();
        
    }
}


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结果:

​19:43:39.303 [main] INFO com.chen.test.JAVA8Features.Demo01 - 我是没有使用Lambda表达式：不简洁、代码多
19:43:39.303 [main] INFO com.chen.test.JAVA8Features.Demo01 - 我是使用Lambda表达式：简洁、灵活

3、Lambda表达式 六种语法格式

Lambda表达式在java语言中引入了一种新的语法元素和操作。
这种操作符号为“->”,
Lambda操作符或箭头操作符，它将Lambda表达式分割为两部分。
左边：指Lambda表达式的所有参数
右边：指Lambda体，即表示Lambda表达式需要执行的功能。

语法格式一：无参数、无返回值，只需要一个Lambda体

package com.chen.test.JAVA8Features;
​
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
​
public class Demo02 {
    private static Logger log = LoggerFactory.getLogger(Demo02.class);
​
    public static void main(String[] args) {
        Runnable t1 = ()-> log.info("Lambda表达式：简洁、灵活，优雅永不过时");
        t1.run();
    }
}



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22:22:39.125 [main] INFO com.chen.test.JAVA8Features.Demo02 - Lambda表达式：简洁、灵活，优雅永不过时
​
Process finished with exit code 0

语法格式二：lambda有一个参数、无返回值

package com.chen.test.JAVA8Features;
​
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
​
import java.util.function.Consumer;
​
public class Demo03 {
    private static Logger log = LoggerFactory.getLogger(Demo03.class);
    public static void main(String[] args) {
        Consumer<String> consumer = new Consumer<String>() {
            @Override
            public void accept(String s) {
                log.info(s);
            }
        };
        consumer.accept("爱与被爱的区别");
​
        Consumer<String> consumer1 = (s) -> log.info(s);
        consumer1.accept("接受爱不一定爱对方，爱一定付出真心爱");
    }
}
​
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23:03:08.992 [main] INFO com.chen.test.JAVA8Features.Demo03 - 爱与被爱的区别
23:03:09.142 [main] INFO com.chen.test.JAVA8Features.Demo03 - 接受爱不一定爱对方，爱一定付出真心爱
​
Process finished with exit code 0

​语法格式三：Lambda只有一个参数时，可以省略（）

package com.chen.test.JAVA8Features;
​
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
​
import java.util.function.Consumer;
​
public class Demo04 {
    private static Logger log = LoggerFactory.getLogger(Demo04.class);
    public static void main(String[] args) {
        Consumer<String> consumer = s -> log.info(s);
        consumer.accept("Lambda只有一个参数时，可以省略（）");
    }
}
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​

23:08:27.295 [main] INFO com.chen.test.JAVA8Features.Demo04 - Lambda只有一个参数时，可以省略（）
​
Process finished with exit code 0

语法格式四：Lambda有两个参数时，并且有返回值

package com.chen.test.JAVA8Features;
​
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
​
import java.util.Comparator;
​
​
public class Demo05 {
    private static Logger log = LoggerFactory.getLogger(Demo05.class);
​
    public static void main(String[] args) {
        CompareOldMethod(12,10);
        findMaxValue(12,10);
        findMinValue(12,10);
    }
//    没有使用Lambda表达式比较大小
    public static void CompareOldMethod(int num1,int num2){
        Comparator<Integer> comparator = new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                log.info("o1:{}",o1);
                log.info("o2:{}",o2);
                return o1 < o2 ? o2 : o1;
            }
        };
        log.info("OldFindMaxValue:{}",comparator.compare(num1,num2));
    }
​
//    使用lambda表达式
    public static void findMaxValue(int num1,int num2){
        Comparator<Integer> comparatorMax = (o1, o2) ->{
​
            log.info("o1:{}",o1);
            log.info("o2:{}",o2);
            return (o1<o2)? o2 :(o1);
        };
​
        log.info("findMaxValue:{}",(comparatorMax.compare(num1,num2)));
​
    }
    public static void findMinValue(int num1,int num2){
        Comparator<Integer> comparatorMin =  (o1, o2) -> {
            log.info("o1:{}",o1);
            log.info("o2:{}",o2);
            return (o1 < o2) ? o1 : o2;
        };
        log.info("FindMinValue:{}",comparatorMin.compare(num1,num2));
    }
}
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​

00:17:10.206 [main] INFO com.chen.test.JAVA8Features.Demo05 - o1:12
00:17:10.206 [main] INFO com.chen.test.JAVA8Features.Demo05 - o2:10
00:17:10.206 [main] INFO com.chen.test.JAVA8Features.Demo05 - OldFindMaxValue:12
00:17:10.315 [main] INFO com.chen.test.JAVA8Features.Demo05 - o1:12
00:17:10.315 [main] INFO com.chen.test.JAVA8Features.Demo05 - o2:10
00:17:10.315 [main] INFO com.chen.test.JAVA8Features.Demo05 - findMaxValue:12
00:17:10.315 [main] INFO com.chen.test.JAVA8Features.Demo05 - o1:12
00:17:10.315 [main] INFO com.chen.test.JAVA8Features.Demo05 - o2:10
00:17:10.315 [main] INFO com.chen.test.JAVA8Features.Demo05 - FindMinValue:10
​
Process finished with exit code 0
​

语法格式五：当Lambda体只有一条语句的时候，return和{}可以省略掉

package com.chen.test.JAVA8Features;
​
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
​
import java.util.Comparator;
​
​
public class Demo05 {
    private static Logger log = LoggerFactory.getLogger(Demo05.class);
​
    public static void main(String[] args) {
        findMaxValue(12,10);
        findMinValue(12,10);
    }
​
//    使用lambda表达式
    public static void findMaxValue(int num1,int num2){
        Comparator<Integer> comparatorMax = (o1, o2) ->{
​
            log.info("o1:{}",o1);
            log.info("o2:{}",o2);
            return (o1<o2)? o2 :(o1);
        };
​
        log.info("findMaxValue:{}",(comparatorMax.compare(num1,num2)));
​
    }
    public static void findMinValue(int num1,int num2){
        Comparator<Integer> comparatorMin =  (o1, o2) -> (o1 < o2) ? o1 : o2;
​
        log.info("FindMinValue:{}",comparatorMin.compare(num1,num2));
    }
}
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​

00:22:31.059 [main] INFO com.chen.test.JAVA8Features.Demo05 - o1:12
00:22:31.075 [main] INFO com.chen.test.JAVA8Features.Demo05 - o2:10
00:22:31.075 [main] INFO com.chen.test.JAVA8Features.Demo05 - findMaxValue:12
00:22:31.075 [main] INFO com.chen.test.JAVA8Features.Demo05 - FindMinValue:10
​
Process finished with exit code 0

语法格式六：类型推断：数据类型可以省略，因为编译器可以推断得出，成为“类型推断”

package com.chen.test.JAVA8Features;
​
import com.mysql.cj.callback.MysqlCallbackHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
​
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.function.Consumer;
​
​
public class Demo07 {
    private static Logger log = LoggerFactory.getLogger(Demo07.class);
​
    public static void main(String[] args) {
        dateType();
    }
​
    public static void dateType(){
        Consumer<String> consumer = (String s) -> log.info(s);
        consumer.accept("Hello World !");
​
        Consumer<String> consumer1 = (s) -> log.info(s);
        consumer1.accept("Hello don't date type !");
    }
}
​
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版本记录

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• 2023-10-18 第一版