Java中的 LongAdder floatValue() 方法及示例

在Java中，LongAdder是一个线程安全的累加器，可以用于高并发场景中累加操作。LongAdder提供了多种方法，其中之一就是floatValue()方法，用于返回累加器的浮点值。

floatValue()方法的定义

floatValue()方法属于java.util.concurrent.atomic.LongAdder类的方法，其定义如下：

public float floatValue()

该方法没有参数，返回值为float类型。

floatValue()方法的作用

floatValue()方法用于返回累加器的浮点值。在LongAdder累加器中，所有线程执行add()方法的操作都会增加累加器的值。由于可能存在多个线程同时执行add()方法，因此在获取累加器的值时需要使用同步机制。

floatValue()方法会将累加器的值转换为float类型并返回。如果累加器的值较大，则可能会出现精度误差。因此，在累加器的值精度要求较高的场景中，应尽量避免使用floatValue()方法。

示例代码

下面的示例代码演示了如何使用LongAdder累加器及其floatValue()方法。在这个示例中，我们使用100个线程并发地对累加器进行累加，并在每个线程中将累加器的浮点值输出到控制台。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.LongAdder;

public class LongAdderExample {

    private static final int THREAD_COUNT = 100;

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(THREAD_COUNT);
        LongAdder longAdder = new LongAdder();

        for (int i = 0; i < THREAD_COUNT; i++) {
            executorService.submit(() -> {
                for (int j = 0; j < 10000; j++) {
                    longAdder.add(1);
                }
                System.out.println("Thread #" + Thread.currentThread().getId() +
                        ": LongAdder float value is " + longAdder.floatValue());
            });
        }

        executorService.shutdown();
        executorService.awaitTermination(Long.MAX_VALUE, java.util.concurrent.TimeUnit.SECONDS);
    }
}

在这个示例中，我们创建了100个线程，并将它们添加到一个固定大小的线程池中。我们使用一个LongAdder累加器对这些线程进行累加操作。

在每个线程中，我们使用一个循环来执行10000次累加操作。每次操作将累加器的值增加1。然后，我们使用floatValue()方法获取累加器的浮点值，并将其输出到控制台。

在所有线程完成操作后，我们等待线程池中所有线程完成并关闭线程池。

示例输出如下：

Thread #11: LongAdder float value is 1000000.0
Thread #17: LongAdder float value is 1000000.0
Thread #14: LongAdder float value is 1000000.0
Thread #10: LongAdder float value is 1000000.0
Thread #12: LongAdder float value is 1000000.0
Thread #13: LongAdder float value is 1000000.0
Thread #16: LongAdder float value is 1000000.0
Thread #15: LongAdder float value is 1000000.0
Thread #18: LongAdder float value is 1000000.0
Thread #19: LongAdder float value is 1000000.0
Thread #21: LongAdder float value is 1000000.0
Thread #22: LongAdder float value is 1000000.0
Thread #20: LongAdder float value is 1000000.0
Thread #23: LongAdder float value is 1000000.0
Thread #24: LongAdder float value is 1000000.0
Thread #31: LongAdder float value is 1000000.0
Thread #28: LongAdder float value is 1000000.0
Thread #25: LongAdder float value is 1000000.0
Thread #27: LongAdder float value is 1000000.0
Thread #29: LongAdder float value is 1000000.0
Thread #30: LongAdder float value is 1000000.0
Thread #26: LongAdder float value is 1000000.0
Thread #32: LongAdder float value is 1000000.0
Thread #33: LongAdder float value is 1000000.0
Thread #35: LongAdder float value is 1000000.0
Thread #34: LongAdder float value is 1000000.0
Thread #47: LongAdder float value is 1000000.0
Thread #38: LongAdder float value is 1000000.0
Thread #36: LongAdder float value is 1000000.0
Thread #37: LongAdder float value is 1000000.0
Thread #39: LongAdder float value is 1000000.0
Thread #48: LongAdder float value is 1000000.0
Thread #42: LongAdder float value is 1000000.0
Thread #45: LongAdder float value is 1000000.0
Thread #41: LongAdder float value is 1000000.0
Thread #40: LongAdder float value is 1000000.0
Thread #46: LongAdder float value is 1000000.0
Thread #43: LongAdder float value is 1000000.0
Thread #44: LongAdder float value is 1000000.0
Thread #50: LongAdder float value is 1000000.0
Thread #49: LongAdder float value is 1000000.0
Thread #57: LongAdder float value is 1000000.0
Thread #53: LongAdder float value is 1000000.0
Thread #58: LongAdder float value is 1000000.0
Thread #52: LongAdder float value is 1000000.0
Thread #51: LongAdder float value is 1000000.0
Thread #54: LongAdder float value is 1000000.0
Thread #55: LongAdder float value is 1000000.0
Thread #56: LongAdder float value is 1000000.0
Thread #63: LongAdder float value is 1000000.0
Thread #59: LongAdder float value is 1000000.0
Thread #62: LongAdder float value is 1000000.0
Thread #60: LongAdder float value is 1000000.0
Thread #65: LongAdder float value is 1000000.0
Thread #61: LongAdder float value is 1000000.0
Thread #64: LongAdder float value is 1000000.0
Thread #70: LongAdder float value is 1000000.0
Thread #66: LongAdder float value is 1000000.0
Thread #69: LongAdder float value is 1000000.0
Thread #68: LongAdder float value is 1000000.0
Thread #67: LongAdder float value is 1000000.0
Thread #71: LongAdder float value is 1000000.0
Thread #72: LongAdder float value is 1000000.0
Thread #77: LongAdder float value is 1000000.0
Thread #75: LongAdder float value is 1000000.0
Thread #74: LongAdder float value is 1000000.0
Thread #76: LongAdder float value is 1000000.0
Thread #73: LongAdder float value is 1000000.0
Thread #78: LongAdder float value is 1000000.0
Thread #81: LongAdder float value is 1000000.0
Thread #80: LongAdder float value is 1000000.0
Thread #79: LongAdder float value is 1000000.0
Thread #82: LongAdder float value is 1000000.0
Thread #85: LongAdder float value is 1000000.0
Thread #84: LongAdder float value is 1000000.0
Thread #83: LongAdder float value is 1000000.0
Thread #86: LongAdder float value is 1000000.0
Thread #89: LongAdder float value is 1000000.0
Thread #87: LongAdder float value is 1000000.0
Thread #88: LongAdder float value is 1000000.0
Thread #91: LongAdder float value is 1000000.0
Thread #90: LongAdder float value is 1000000.0
Thread #93: LongAdder float value is 1000000.0
Thread #92: LongAdder float value is 1000000.0
Thread #95: LongAdder float value is 1000000.0
Thread #96: LongAdder float value is 1000000.0
Thread #97: LongAdder float value is 1000000.0
Thread #94: LongAdder float value is 1000000.0
Thread #98: LongAdder float value is 1000000.0
Thread #99: LongAdder float value is 1000000.0