为什么这两段Java代码产生2个不同的结果？

Question

    int secs_per_day = 24 * 60 * 60;

    int LIGHTSPEED = 186000;        // 186,000 mi/sec speed of light

    long miles_traveled = secs_per_day * LIGHTSPEED;

    System.out.println("Miles traveled by light in a day: " + miles_traveled);

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    long secs_per_day = 24 * 60 * 60;

    long LIGHTSPEED = 186000;       // 186,000 mi/sec speed of light

    long miles_traveled = secs_per_day * LIGHTSPEED;

    System.out.println("Miles traveled by light in a day: " + miles_traveled);