常用的函数式接口

1. Supplier接口

生产性接口，指定接口中的泛型为是什么类型，那么接口中的get方法就会产生什么类型的数据。

例1：输出字符串

package cn.itcast.day_13;

import java.util.function.Supplier;

public class DemoSupplier {
    public static String getString(Supplier<String> sup){
        return sup.get();
    }

    public static void main(String[] args) {
        String s = getString(() -> {
            //生产一个字符串并返回
            return "aaaa";
        });
        System.out.println(s);
    }
}

例2：求数组中最大的数

package cn.itcast.day_13;

import java.util.function.Supplier;

public class DemoSupplier02 {
    public static int getMax(Supplier<Integer> sup){
        return sup.get();
    }

    public static void main(String[] args) {
        int[] arr = {3, 1, 4, 7, 2, 8};
        //调用getMax方法
        int maxvalue = getMax(() -> {
            int max = arr[0];
            for (int i = 0; i < arr.length; i++) {
                if (max < arr[i]){
                    max = arr[i];
                }
            }
            return max;
        });

        System.out.println("最大值是" + maxvalue);
    }
}

2. Consumer接口

例1：对字符串进行反转

package cn.itcast.day_13;

import java.util.function.Consumer;

public class DemoConsumer {

    public static void method(String name, Consumer<String> con){
        con.accept(name);
    }

    public static void main(String[] args) {
        method("abc",(String name)->{
            //对传递的字符串进行消费
            //1.直接输出
            System.out.println(name);

            //2.字符串反转
            String rename = new StringBuffer(name).reverse().toString();
            System.out.println(rename);
        });
    }
}

Consum接口中的andThen方法：

（1）传入两个Consumer接口实现大小写转换：

package cn.itcast.day_13;

import java.util.function.Consumer;

public class DemoandThen {
    public static void method(String s, Consumer<String> con1, Consumer<String> con2){
 7         con1.accept(s);
 8         con2.accept(s);
    }

    public static void main(String[] args) {
        method("hello", (String s)->{
            System.out.println(s.toUpperCase());
        }, (String s)->{
            System.out.println(s.toLowerCase());
        });
    }
}

（2）使用andThen方法实现大小写转换

package cn.itcast.day_13;

import java.util.function.Consumer;

public class DemoandThen {
    public static void method(String s, Consumer<String> con1, Consumer<String> con2){
        //先对con1进行消费，再对con2进行消费
        con1.andThen(con2).accept(s);
    }

    public static void main(String[] args) {
        method("hello", (String s)->{
            System.out.println(s.toUpperCase());
        }, (String s)->{
            System.out.println(s.toLowerCase());
        });
    }
}

 使用andThen方法实现格式化输入

package cn.itcast.day_13;

import java.util.function.Consumer;

public class DemoConsumer02 {
    public static void method(String[] arr, Consumer<String> con1, Consumer<String> con2){
        for (String message : arr){
            //使用andThen方法连接
            con1.andThen(con2).accept(message);
        }
    }

    public static void main(String[] args) {
        String[] arr = {"张三,男", "李四,女", "王五,男"};
        method(arr, (message)->{
            //消费方式
            String name = message.split(",")[0];
            System.out.print("姓名:"+name);
            System.out.print("---");
        }, (message)->{
            String xingbie = message.split(",")[1];
            System.out.print("性别:"+xingbie+"
");
        });
    }
}

3. Predicate接口

用于对某种数据进行判断，返回一个boolean类型

例：判断一个字符串长度是否大于5

package cn.itcast.day_14;

import java.util.function.Predicate;

public class PredicateDemo {
    public static boolean checkString(String s, Predicate<String> pre){
        return pre.test(s);
    }

    public static void main(String[] args) {
        String s = "abcdef";
        boolean b = checkString(s, (String str) -> {
            //对参数传递的字符串进行判断，判断长度是否大于5
            return str.length() > 5;
        });

        System.out.println(b);
    }
}

predicate中的三个默认方法

（1）and方法：

例1：判断字符串长度是否大于5且包含a

package cn.itcast.day_14;

import java.util.function.Predicate;

public class PredicateDemo02 {
    public static boolean checkString(String s, Predicate<String> pre1, Predicate<String> pre2){
        return pre1.and(pre2).test(s);
    }

    public static void main(String[] args) {
        String s = "abcdef";
        boolean b = checkString(s, (String str) -> {
             return str.length() > 5;
        }, (String str) -> {
            return  str.contains("a");
        });
        System.out.println(b);
    }
}

（2）or方法：

例2：判断字符串长度是否大于5或包含a

package cn.itcast.day_14;

import java.util.function.Predicate;

public class PredicateDemo03 {
    public static boolean checkString(String s, Predicate<String> pre1, Predicate<String> pre2){
        return pre1.or(pre2).test(s);
    }

    public static void main(String[] args) {
        String s = "abcdef";
        boolean b = checkString(s, (String str) -> {
            return str.length() > 5;
        }, (String str) -> {
            return str.contains("a");
        });
        System.out.println(b);
    }
}

 （3）！：

例3：判断字符串长度不大于5

package cn.itcast.day_14;

import java.util.function.Predicate;

public class PredicateDemo04 {
    public static boolean checkString(String s, Predicate<String> pre){
        return !pre.test(s);
    }

    public static void main(String[] args) {
        String s = "abcdef";
        boolean b = checkString(s, (String str) -> {
            return str.length() > 5;
        });
        System.out.println(b);
    }
}

例4：过滤数据

package cn.itcast.day_14;

import java.util.ArrayList;
import java.util.function.Predicate;
import java.util.zip.ZipEntry;

public class PredicateDemo05 {
    public static ArrayList<String> filter(String[] arr, Predicate<String> pre1, Predicate<String> pre2){
        //定义一个Arrarlist集合
        ArrayList<String> list = new ArrayList<>();
        //获取数组中的每一条信息
        for (String s : list){
            boolean b = pre1.and(pre2).test(s);
            if (b){
                list.add(s);
            }
        }
        return list;
    }

    public static void main(String[] args) {
        String[] arr = {"张三,男","李四,女","王五,男","赵六,女"};
        ArrayList<String> list = filter(arr, (String str) -> {
            //获取字符串中性别，判断是否为女
            return str.split(",")[1].equals("女");
        }, (String str) -> {
            return str.split(",")[0].length() == 4;
        });

        for (String s : list){
            System.out.println(s);
        }
    }
}

4. Function接口

例1：实现字符串转换为数字

package cn.itcast.day_14;

import java.util.function.Function;

public class FunctionDemo {
    public static void change(String s, Function<String,Integer> fun){
        Integer in = fun.apply(s);
        System.out.println(in);
    }

    public static void main(String[] args) {
        String s = "1234";
        change(s, (String str)->{
            return Integer.parseInt(str);
        });
    }
}

Function接口中的andThen方法

例2：将字符串转为数字，加10后再转换为字符串

package cn.itcast.day_14;

import java.util.function.Function;

public class FunctionDemo02 {
    public static void change(String s, Function<String,Integer> fun1, Function<Integer,String> fun2){
        String s1 = fun1.andThen(fun2).apply(s);
        System.out.println(s1);
    }

    public static void main(String[] args) {
        String s = "123";
        change(s, (String str)->{
            //将字符转换为整数
            return Integer.parseInt(str) + 10;
        },(Integer in)->{
            //数字转换为字符串
            return in+"";
        });
    }
}

例3：