Timer.java

class Timer {
    private long startNanoTime, endNanoTime = 0L;

    void start() {
        this.startNanoTime = System.nanoTime();
    }
    
    void stop() {
        if (startNanoTime != 0L) {
            this.endNanoTime = System.nanoTime();
        } else {
            throw new IllegalStateException();
        }
    }
    
    String getResultTimeInMilliseconds() {
        long resultTime = (endNanoTime - startNanoTime) / 1000000;
        startNanoTime = 0L;
        endNanoTime = 0L;
        return "計測時間：" + resultTime + "ms";
    }
}