我们正在做以下的编程练习：[Death by Coffee][1]。
主要任务是将整数转换为十六进制并进行值的相加。我们编写了以下代码：
    public class Dinglemouse {
    
      public static int[] coffeeLimits /*☕*/ (final int year, final int month, final int day) {
        System.out.println("year: "+year);
        System.out.println("month: "+month);
        System.out.println("day: "+day);
        
        long healthNumber = Long.parseLong(String.valueOf(year)+String.valueOf(month)+String.valueOf(day));
        System.out.println("healthNumber: "+healthNumber);
        
        long cafe = Long.valueOf("CAFE",16);
        long decaf = Long.valueOf("DECAF",16);
        
        int cafeLimit = getLimit(cafe, healthNumber);
        System.out.println("\ncafeLimit: "+cafeLimit);
        int decafLimit = getLimit(decaf, healthNumber);
        System.out.println("\ndecafLimit: "+decafLimit);
        
        return new int []{cafeLimit, decafLimit};
      }
    
      public static int getLimit(long coffee, long healthNumber){
        int limit=0;
        while(limit<=5000 && !Long.toHexString(healthNumber).contains("dead")){
          limit++;
          healthNumber+=coffee;
          System.out.println("new healthNumber: "+Long.toHexString(healthNumber));
        }
        return limit>5000 ? 0 : limit;    
      }
    
    }
我们想知道为什么代码通过以下的测试，除了 exJohn：
    import org.junit.Test;
    import static org.junit.Assert.*;
    import java.util.*;
    
    public class Tests {
      
      // Show returned limits
      private static int[] show(final int y, final int m, final int d, final int[] result) {
        System.out.println(String.format("%4d%02d%02d -> ",y,m,d)+Arrays.toString(result));
        return result;
      }
      
      @Test
      public void exJohn() {
        final int y=1950, m=1, d=19;
        assertArrayEquals(new int[]{2645,1162}, show(y,m,d,Dinglemouse.coffeeLimits(y,m,d)));
      }
      
      @Test
      public void exSusan() {
        final int y=1965, m=12, d=11;
        assertArrayEquals(new int[]{111,0}, show(y,m,d,Dinglemouse.coffeeLimits(y,m,d)));
      }
    
      @Test
      public void exElizabeth() {
        final int y=1964, m=11, d=28;
        assertArrayEquals(new int[]{0,11}, show(y,m,d,Dinglemouse.coffeeLimits(y,m,d)));
      }
    
      @Test
      public void exPeter() {
        final int y=1965, m=9, d=4;
        assertArrayEquals(new int[]{0,0}, show(y,m,d,Dinglemouse.coffeeLimits(y,m,d)));
      }
      
    }
我们已经打印出在 `getLimit` 循环内部得到的内容，我们发现咖啡限制的最后一个 `healthNumber` 输出为：
    ...
    new healthNumber: 2dc4cbb
    new healthNumber: 2dd17b9
    new healthNumber: 2dde2b7
    new healthNumber: 2deadb5
    
    cafeLimit: 889
而对于无咖啡因限制，我们有：
    ...
    new healthNumber: 10ff8a241
    new healthNumber: 110068ef0
    new healthNumber: 110147b9f
    new healthNumber: 11022684e
    
    decafLimit: 0
因此，我们的代码结果是：
[889, 0]
而实际上应该是：
[2645, 1162]
我们认为可能是整数溢出导致的，因此我们将所有变量都更改为 long，但程序的行为仍然相同。
我们已阅读过：
 - [https://stackoverflow.com/questions/9321553/java-convert-integer-to-hex-integer](https://stackoverflow.com/questions/9321553/java-convert-integer-to-hex-integer)
 - [https://stackoverflow.com/questions/5258415/how-to-get-a-hex-value-from-a-decimal-integer-in-java](https://stackoverflow.com/questions/5258415/how-to-get-a-hex-value-from-a-decimal-integer-in-java)
 - [https://stackoverflow.com/questions/11194513/convert-hex-string-to-int](https://stackoverflow.com/questions/11194513/convert-hex-string-to-int)
  [1]: [https://www.codewars.com/kata/57db78d3b43dfab59c001abe](https://www.codewars.com/kata/57db78d3b43dfab59c001abe)

long healthNumber = Long.parseLong(String.valueOf(year)+String.valueOf(month)+String.valueOf(day));

long healthNumber = year*10000+month*100+day;