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四大函数式接口

HeJin大约 2 分钟JavaJUC并发编程

新时代的程序员：lambda表达式、链式编程、函数式接口、Stream流式计算。

image-20210312150812780
image-20210312150812780

函数式接口。只有一个方法的接口。简化编程模型，在新版本的框架底层大量应用。

@FunctionalInterface
public interface Runnable {
    /**
     * When an object implementing interface <code>Runnable</code> is used
     * to create a thread, starting the thread causes the object's
     * <code>run</code> method to be called in that separately executing
     * thread.
     * <p>
     * The general contract of the method <code>run</code> is that it may
     * take any action whatsoever.
     *
     * @see     java.lang.Thread#run()
     */
    public abstract void run();
}

Function函数型接口

image-20210312151401580
image-20210312151401580
public class Demo01 {
    public static void main(String[] args) {
        Function function = new Function<String, String>() {
            @Override
            public String apply(String str) {
                return str;
            }
        };

        System.out.println(function.apply("123"));
    }
}

123

Process finished with exit code 0
  • 有一个输入参数，有一个输出
  • 可以用lambda表达式简化
public class Demo01 {
    public static void main(String[] args) {
        Function function = (str) -> {
            return str;
        };

        System.out.println(function.apply("123"));
    }
}

Predicate断定型接口

image-20210312152329093
image-20210312152329093
public class Demo02 {
    public static void main(String[] args) {
        /**
         * 判断字符串是否为空
         */
        Predicate predicate = new Predicate<String>() {
            @Override
            public boolean test(String str) {
                return str.isEmpty();
            }
        };

        System.out.println(predicate.test("123"));
    }
}

false

Process finished with exit code 0

  • 断定型接口：有一个输入参数，返回值只能是布尔值。

  • 可以用lambda表达式简化。

public class Demo02 {
    public static void main(String[] args) {
        /**
         * 判断字符串是否为空
         */
        Predicate<String> predicate = (str) -> {
            return str.isEmpty();
        };

        System.out.println(predicate.test("123"));
    }
}

Consumer消费型接口

image-20210312153202460
image-20210312153202460
public class Demo03 {
    public static void main(String[] args) {
        Consumer consumer = new Consumer<String>() {
            @Override
            public void accept(String str) {
                System.out.println(str);
            }
        };

        consumer.accept("123");
    }
}

123

Process finished with exit code 0

消费型接口：只有输入，没有返回值。

可以用lambda表达式简化。

public class Demo03 {
    public static void main(String[] args) {
        Consumer consumer = (str) -> {
            System.out.println(str);
        };

        consumer.accept("123");
    }
}

Supplier供给型接口

image-20210312153645620
image-20210312153645620
public class Demo04 {
    public static void main(String[] args) {
        Supplier supplier = new Supplier<Integer>() {
            @Override
            public Integer get() {
                System.out.println("get()");
                return 1024;
            }
        };

        System.out.println(supplier.get());
    }
}

get()
1024

Process finished with exit code 0

供给型接口：没有参数，只有返回值。

可以用lambda表达式简化。

public class Demo04 {
    public static void main(String[] args) {
        Supplier supplier = () -> {
            System.out.println("get()");
            return 1024;
        };

        System.out.println(supplier.get());
    }
}
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