java编写增量整数供应商

Question

我试图掌握一些Java 8函数式编程。我试图“从功能上”写下面的IntSupplier，但我一直遇到问题

import java.util.function.IntSupplier;

    @Test public void test_nonFunctional() {
        IntSupplier supplier = new IntSupplier() {
            private int nextInt = 0;
            @Override public int getAsInt() {
                return nextInt++;
            }
        };
    }

以下是我的尝试。这些问题在代码中标记为注释

import org.junit.Test;

import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.IntSupplier;

public class IntSupplierTest {
    @Test public void test_nonFunctional() {
        IntSupplier supplier = new IntSupplier() {
            private int nextInt = 0;
            @Override public int getAsInt() { return nextInt++; }
        }; // Works but is not functional.
    }

    @Test public void test_naive() {
        int nextInt = 0;
        IntSupplier supplier = () -> nextInt++; // Doesn't compile: requires nextInt to be final.
    }

    @Test public void test_nextIntIsFinal() {
        final int nextInt = 0;
        IntSupplier supplier = () -> nextInt++; // Doesn't compile: nextInt can't be incremented because it's final.
    }

    @Test public void test_useWrapper() {
        final AtomicInteger nextInt = new AtomicInteger(0);
        IntSupplier supplier = () -> nextInt.getAndIncrement(); // It is not the same as my original question as this test uses an extra object.
    }
}

如果答案很简单，不使用额外的对象就无法完成，请直接说出来

Answer 1

你可以这样做：

IntSupplier supplier = new AtomicInteger(0)::incrementAndGet;