java 8 Consumer 接口
java 8中開始支持函數式編程，初接觸後很不適應，因爲和對象的思想相差太多。在某次項目中學習了scala之後再返回來看java 8中的函數，有種似曾相識的感覺。java也在和其他語言的競爭中不斷更新自己。先來看源碼：
@FunctionalInterface
public interface Consumer<T> {
/**
* 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<T> andThen(Consumer<? super T> after) {
Objects.requireNonNull(after);
return (T t) -> { accept(t); after.accept(t); };
}
}
只有兩個方法，accept() 和 andThen(); consumer接受單值，沒有返回值，對傳入的值做操作，或者做判斷業務。consumer是lambda表達式的類型。
public class ConsumerTest {
@Test
public void testAccept(){
// 判斷值
Consumer<Integer> first = x -> {
if(x % 2 == 0){
System.out.println("偶數");
} else {
System.out.println("奇數");
}
};
first.accept(3);
}
@Test
public void testAndThen(){
// andThen操作，先consumer1再執行consumer2,源碼中的after參數
Consumer<Integer> consumer1 = x -> System.out.println(x + x);
Consumer<Integer> consumer2 = x -> System.out.println(x * x);
consumer1.andThen(consumer2).accept(3);
}
}
網上介紹的文章很多，上面只是簡單的做了一個例子操作。有一個例子還可以的，寫在後面