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四大函数式接口

函数式接口：只有一个方法的接口 ，例如：Runnable接口

Function

函数型接口，有一个输入参数，有一个输出

源码：

/*** Represents a function that accepts one argument and produces a result.** This is a functional interface* whose functional method is apply(Object).** @param <T> the type of the input to the function* @param <R> the type of the result of the function** @since 1.8*/
@FunctionalInterface
public interface Function<T, R> {/*** Applies this function to the given argument.** @param t the function argument* @return the function result*/R apply(T t);

示例：

package function;import java.util.function.Function;/**** Function 函数型接口，有一个输入参数，有一个输出* 只要是函数式接口，就可以用lambda表达式*/
public class Demo01 {public static void main(String[] args) {// 匿名内部类，工具类，输出输入的结果
//        Function function = new Function<String,String>() {
//            @Override
//            public String apply(String s) {
//
//                return null;
//            }
//        };// 使用lambda表达式Function function = (str)->{return str;};System.out.println(function.apply("abc"));}
}

Predicate

断定型接口：只有一个输入参数，返回值为boolean

源码：

/*** Represents a predicate (boolean-valued function) of one argument.** This is a functional interface* whose functional method is test(Object).** @param <T> the type of the input to the predicate** @since 1.8*/
@FunctionalInterface
public interface Predicate<T> {/*** Evaluates this predicate on the given argument.** @param t the input argument* @return {@code true} if the input argument matches the predicate,* otherwise {@code false}*/boolean test(T t);

示例

package function;import java.util.function.Predicate;/**** 断定型接口：有一个输入参数，返回值为boolean*/
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 s) {
//                return s.isEmpty();
//            }
//        };// 函数型接口+lambda表达式，使代码看起来更加简洁Predicate<String> predicate = (s)->{return s.isEmpty();};System.out.println(predicate.test(""));}
}

Consumer

消费型接口，有一个参数，没有返回值

源码：

/*** Represents an operation that accepts a single input argument and returns no* result. Unlike most other functional interfaces, {@code Consumer} is expected* to operate via side-effects.** <p>This is afunctional interface* whose functional method is accept(Object).** @param <T> the type of the input to the operation** @since 1.8*/
@FunctionalInterface
public interface Consumer<T> {/*** Performs this operation on the given argument.** @param t the input argument*/void accept(T t);

示例

package function;import javax.lang.model.element.NestingKind;
import java.util.function.Consumer;/**** Consumer 消费型接口：只有输入，没有返回值*/
public class Demo03 {public static void main(String[] args) {
//        Consumer<String> consumer = new Consumer<String>() {
//            @Override
//            public void accept(String s) {
//                System.out.println(s);
//            }
//        };Consumer<String> consumer = (s)->{System.out.println(s);};consumer.accept("asd");}
}

Supplier

供给型接口：没有参数，只有返回值

源码：

/*** Represents a supplier of results.** There is no requirement that a new or distinct result be returned each* time the supplier is invoked.** <This is a functional interface* whose functional method isget().** @param <T> the type of results supplied by this supplier** @since 1.8*/
@FunctionalInterface
public interface Supplier<T> {/*** Gets a result.** @return a result*/T get();
}

示例

package function;import java.util.function.Supplier;/**** 供给型接口：没有参数，只有返回值*/
public class Demo04 {public static void main(String[] args) {
//        Supplier<Integer> supplier = new Supplier<Integer>() {
//
//            @Override
//            public Integer get() {
//                return 1024;
//            }
//        };Supplier<Integer> supplier  = ()->{return 1024;};System.out.println(supplier.get());}
}

为什么要学习函数式接口？

• 简化编程模型，使代码更加可读易懂

• 在新版本的框架底层中，函数式接口有大量的应用