Java常用的函数式接口

Posted 2021-03-16 路上的风景

package com.fgy.demo3;

import java.util.function.Supplier;

/**
 * 函数式接口：Supplier
 * get方法返回和泛型相同类型的值
 */
public class Demo01Supplier {
    public static void main(String[] args) {
        String s = getString(() -> "胡歌");
        System.out.println(s);

        int[] arr = {10, 11, 45, 12, 90};
        int maxValue = getMax(() -> {
            int max = arr[0];
            for (int i = 1; i < arr.length; i++) {
                if (max < arr[i]) {
                    max = arr[i];
                }
            }
            return max;
        });
        System.out.println(maxValue);
    }

    // 返回int类型的值
    private static int getMax(Supplier<Integer> sup) {
        return sup.get();
    }

    // 返回String类型的值
    private static String getString(Supplier<String> sup) {
        return sup.get();
    }
}

package com.fgy.demo3;

import java.util.function.Consumer;

/**
 * 函数式接口：Consumer
 * accept方法使用和泛型相同类型的值
 */
public class Demo02Consumer {
    public static void main(String[] args) {
        method("胡歌", name -> {
            // System.out.println(name);
            // 反转字符串
            String reName = new StringBuilder(name).reverse().toString();
            System.out.println(reName);
        });
    }

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

package com.fgy.demo3;

import java.util.function.Consumer;

/**
 * 函数式接口：Consumer的默认方法andThen
 * 作用：需要两个Consumer接口，可以把两个Consumer接口组合到一起，再对数据进行消费
 */
public class Demo03ConsumerAndThen {
    public static void main(String[] args) {
        method("Hello Word",
                s -> System.out.println(s.toUpperCase()),
                s -> System.out.println(s.toLowerCase())
        );

        String[] arr = {"赵丽颖,女", "胡歌,男", "李泌,女"};
        printInfo(arr,
                s -> System.out.print("姓名：" + s.split(",")[0]),
                s -> System.out.println(" 性别：" + s.split(",")[1])
        );
    }

    private static void method(String s, Consumer<String> con1, Consumer<String> con2) {
        // con1.accept(s);
        // con2.accept(s);

        con1.andThen(con2).accept(s); // HELLO WORD
                                      // hello word
        System.out.println("-----------");
        con2.andThen(con1).accept(s); // hello word
                                      // HELLO WORD
    }

    /**
     * 格式化信息输出
     */
    private static void printInfo(String[] arr, Consumer<String> con1, Consumer<String> con2){
        for (String s : arr) {
            con1.andThen(con2).accept(s);
        }
    }
}

package com.fgy.demo3;

import java.util.function.Predicate;

/**
 * 函数式接口：Predicate
 * Test(T t)用来对指定类型的数据进行判断，符合条件返回true，不符合返回false
 */
public class Demo04Predicate {
    public static void main(String[] args) {
        boolean bool = checkString("abc", s -> s.length() >= 5);
        System.out.println(bool);
    }

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

package com.fgy.demo3;

import java.util.function.Predicate;

/**
 * 函数式接口：Predicate的默认方法and
 * 表示并且关系，用来连接两个判断条件，相当于&&运算符
 */
public class Demo05PredicateAnd {
    public static void main(String[] args) {
        boolean bool = checkString("abc",
                s -> s.length() >= 5,
                s -> s.contains("a")
        );
        System.out.println(bool);
    }

    private static boolean checkString(String s, Predicate<String> pre1, Predicate<String> pre2) {
        // return pre1.test(s) && pre2.test(s);
        return pre1.and(pre2).test(s);
    }
}

package com.fgy.demo3;

import java.util.function.Predicate;

/**
 * 函数式接口：Predicate的默认方法or
 * 表示或者关系，用来连接两个判断条件，相当于||运算符
 */
public class Demo06PredicateOr {
    public static void main(String[] args) {
        boolean bool = checkString("ab",
                s -> s.length() >= 5,
                s -> s.contains("a")
        );
        System.out.println(bool);
    }

    private static boolean checkString(String s, Predicate<String> pre1, Predicate<String> pre2) {
        // return pre1.test(s) || pre2.test(s);
        return pre1.or(pre2).test(s);
    }
}

package com.fgy.demo3;

import java.util.function.Predicate;

/**
 * 函数式接口：Predicate的默认方法negate
 * 表示取反，相当!运算符
 */
public class Demo07PredicateNegate {
    public static void main(String[] args) {
        boolean bool = checkString("abc", s -> s.length() >= 5);
        System.out.println(bool);
    }

    private static boolean checkString(String s, Predicate<String> pre) {
        // return !pre.test(s);
        return pre.negate().test(s);
    }
}

package com.fgy.demo3;

import java.util.function.Function;

/**
 * 函数式接口：Function
 * R apply(T t)根据类型T的参数获取类型R的结果
 */
public class Demo08Function {
    public static void main(String[] args) {
        change("1234", s -> Integer.parseInt(s));
    }

    /**
     * Function<String, Integer>
     * 把String类型转换为Integer
     */
    private static void change(String s, Function<String, Integer> fun) {
        Integer in = fun.apply(s);
        System.out.println(in);
    }
}

package com.fgy.demo3;

import java.util.function.Function;

/**
 * 函数式接口：Function的默认方法andThen
 */
public class Demo08FunctionAndThen {
    public static void main(String[] args) {
        change("10",
                s -> Integer.parseInt(s) + 10,
                i -> "String:" + String.valueOf(i)
        );
    }

    private static void change(String s, Function<String, Integer> fun1, Function<Integer, String> fun2) {
        // Integer in = fun1.apply(s) + 10; // 20
        // String ss = "String" + fun2.apply(in); // String:20

        String ss = fun1.andThen(fun2).apply(s);
        System.out.println(ss);
    }
}