Java8 Supplier接口和Consumer接口原理解析

java8 Supplier接口和Consumer接口原理解析

Supplier接口

package java.util.function;

/**

* 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 is {@link #get()}.

*

* @param the type of results supplied by this supplier

*

* @since 1.8

*/

@FunctionalInterface

public interface Supplier {

/**

* Gets a result.

*

* @return a result

*/

T get();

}

supplier接口只有一个抽象方法get(),通过get方法产生一个T类型实例。

实例：

package me.yanand;

import jalHpiYNNqWva.util.function.Supplier;

public class TestSupplier {

public static void main(String[] args) {

Supplier appleSupplier = Apple::new;

System.out.println("--------");

appleSupplier.get();

}

}

class Apple{

public Apple() {

System.out.prihttp://ntln("创建实例");

}

}

Consumer接口

package java.util.function;

import java.util.Objects;

/**

* 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.

*

*

This is a functional interface

* whose functional method is {@link #accept(Object)}.

*

* @param the type of the input to thhttp://e operation

*

* @since 1.8

*/

@FunctionalInterface

public interface Consumer {

/**

* Performs this operation on the given argument.

*

* @param t the input argument

*/

void accept(T t);

/**

* Returns a composed {@code Consumer} that performs, in sequence, this

* operation followed by the {@code after} operation. If performing either

* operation throws an exception, it is relayed to the caller of the

* composed operation. If performing this operation throws an exception,

* the {@code after} operation will not be performed.

*

* @param after the operation to perform after this operation

* @return a composed {@code Consumer} that performs in sequence this

* operation followed by the {@code after} operation

* @throws NullPointerException if {@code after} is null

*/

default Consumer andThen(Consumer super T> after) {

Objects.requireNonNull(after);

return (T t) -> { accept(t); after.accept(t); };

}

}

一个抽象方法accept(T t)定义了要执行的具体操作；注意看andThen方法，接收Consumer super T>类型参数，返回一个lambda表达式，此表达式定义了新的执行过程，先执行当前Consumer实例的accept方法，再执行入参传进来的Consumer实例的accept方法，这两个accept方法接收都是相同的入参t。

实例：

package me.yanand;

import java.util.function.Consumer;

public class TestConsumer {

public static void main(String[] args) {

Consumer consumer = (t) -> {

System.out.println(t*3);

};

Consumer consumerAfter = (s) -> {

System.out.println("之后执行："+s);

};

consumer.andThen(consumerAfter).accept(5);

}

}

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