当你增加一个整数超过它的最大值时会发生什么？

在Java中，当你增加一个int（或者byte / short / long）超过它的最大值时会发生什么？ 它是否环绕到最大负值？

AtomicInteger.getAndIncrement（）是否也以相同的方式performance？

Answer 1

从整数操作的Java语言规范部分 ：

内置的整数运算符不会以任何方式指示上溢或下溢。

结果由语言指定，并独立于JVM版本： Integer.MAX_VALUE + 1 == Integer.MIN_VALUE和Integer.MIN_VALUE - 1 == Integer.MAX_VALUE 。 其他整数types也是如此。

primefaces整数对象（ AtomicInteger ， AtomicLong等）在内部使用正常的整型运算符，所以getAndDecrement()等也是这样。

Answer 2

如果你做这样的事情：

 int x = 2147483647; x++; 

如果你现在打印出x，它将是值-2147483648

Answer 3

正如jterrace所说，Java运行时将“结果”为-2147483648的Integer.MIN_VALUE。

但是这在math上是不正确的！ 正确的math答案是2147483648.但是“int”不能有2147483648的值。“int”的边界是-2147483648到2147483647

那么为什么Java不会抛出exception呢？ 好问题！ 一个数组对象会。

但是语言作者知道他们原始types的范围，所以他们使用“包装”技术来避免代价高昂的exception。

作为开发人员，您必须testing这些types的边界。 增加一个简单的testing将是

 if(x++ == Integer.MIN_VALUE) //boundary exceeded 

一个简单的递减testing将是

 if(x-- == Integer.MAX_VALUE) //boundary exceeded 

一个完整的testing将是

 if(x++ == Integer.MIN_VALUE || x-- == Integer.MAX_VALUE) //boundary exceeded 

Answer 4

会发生什么是一个额外的位被添加到最右边的位，顺序递减作为一个负符号int …注意'int_32'后发生了什么;

  int _0 = 0b0000000000000000000000000000000; int _1 = 0b0000000000000000000000000000001; int _2 = 0b0000000000000000000000000000010; int _3 = 0b0000000000000000000000000000100; int _4 = 0b0000000000000000000000000001000; int _5 = 0b0000000000000000000000000010000; int _6 = 0b0000000000000000000000000100000; int _7 = 0b0000000000000000000000001000000; int _8 = 0b0000000000000000000000010000000; int _9 = 0b0000000000000000000000100000000; int _10 = 0b0000000000000000000001000000000; int _11 = 0b0000000000000000000010000000000; int _12 = 0b0000000000000000000100000000000; int _13 = 0b0000000000000000001000000000000; int _14 = 0b0000000000000000010000000000000; int _15 = 0b0000000000000000100000000000000; int _16 = 0b0000000000000001000000000000000; int _17 = 0b0000000000000010000000000000000; int _18 = 0b0000000000000100000000000000000; int _19 = 0b0000000000001000000000000000000; int _20 = 0b0000000000010000000000000000000; int _21 = 0b0000000000100000000000000000000; int _22 = 0b0000000001000000000000000000000; int _23 = 0b0000000010000000000000000000000; int _24 = 0b0000000100000000000000000000000; int _25 = 0b0000001000000000000000000000000; int _26 = 0b0000010000000000000000000000000; int _27 = 0b0000100000000000000000000000000; int _28 = 0b0001000000000000000000000000000; int _29 = 0b0010000000000000000000000000000; int _30 = 0b0100000000000000000000000000000; int _31 = 0b1000000000000000000000000000000; int _32 = 0b1111111111111111111111111111111; int _XX = 0b10000000000000000000000000000000; // numeric overflow. int _33 = 0b10000000000000000000000000000001; int _34 = 0b11000000000000000000000000000000; int _35 = 0b11100000000000000000000000000000; int _36 = 0b11110000000000000000000000000000; int _37 = 0b11111000000000000000000000000000; int _38 = 0b11111100000000000000000000000000; int _39 = 0b11111110000000000000000000000000; int _40 = 0b11111111000000000000000000000000; int _41 = 0b11111111100000000000000000000000; int _42 = 0b11111111110000000000000000000000; int _43 = 0b11111111111000000000000000000000; int _44 = 0b11111111111100000000000000000000; int _45 = 0b11111111111110000000000000000000; int _46 = 0b11111111111111000000000000000000; int _47 = 0b11111111111111100000000000000000; int _48 = 0b11111111111111110000000000000000; int _49 = 0b11111111111111111000000000000000; int _50 = 0b11111111111111111100000000000000; int _51 = 0b11111111111111111110000000000000; int _52 = 0b11111111111111111111000000000000; int _53 = 0b11111111111111111111100000000000; int _54 = 0b11111111111111111111110000000000; int _55 = 0b11111111111111111111111000000000; int _56 = 0b11111111111111111111111100000000; int _57 = 0b11111111111111111111111110000000; int _58 = 0b11111111111111111111111111000000; int _59 = 0b11111111111111111111111111100000; int _60 = 0b11111111111111111111111111110000; int _61 = 0b11111111111111111111111111111000; int _62 = 0b11111111111111111111111111111100; int _63 = 0b11111111111111111111111111111110; int _64 = 0b11111111111111111111111111111111; System.out.println( " _0 = " + _0 ); System.out.println( " _1 = " + _1 ); System.out.println( " _2 = " + _2 ); System.out.println( " _3 = " + _3 ); System.out.println( " _4 = " + _4 ); System.out.println( " _5 = " + _5 ); System.out.println( " _6 = " + _6 ); System.out.println( " _7 = " + _7 ); System.out.println( " _8 = " + _8 ); System.out.println( " _9 = " + _9 ); System.out.println( " _10 = " + _10 ); System.out.println( " _11 = " + _11 ); System.out.println( " _12 = " + _12 ); System.out.println( " _13 = " + _13 ); System.out.println( " _14 = " + _14 ); System.out.println( " _15 = " + _15 ); System.out.println( " _16 = " + _16 ); System.out.println( " _17 = " + _17 ); System.out.println( " _18 = " + _18 ); System.out.println( " _19 = " + _19 ); System.out.println( " _20 = " + _20 ); System.out.println( " _21 = " + _21 ); System.out.println( " _22 = " + _22 ); System.out.println( " _23 = " + _23 ); System.out.println( " _24 = " + _24 ); System.out.println( " _25 = " + _25 ); System.out.println( " _26 = " + _26 ); System.out.println( " _27 = " + _27 ); System.out.println( " _28 = " + _28 ); System.out.println( " _29 = " + _29 ); System.out.println( " _30 = " + _30 ); System.out.println( " _31 = " + _31 ); System.out.println( " _32 = " + _32 ); System.out.println( " _xx = " + _xx ); // -2147483648 System.out.println( " _33 = " + _33 ); System.out.println( " _34 = " + _34 ); System.out.println( " _35 = " + _35 ); System.out.println( " _36 = " + _36 ); System.out.println( " _37 = " + _37 ); System.out.println( " _38 = " + _38 ); System.out.println( " _39 = " + _39 ); System.out.println( " _40 = " + _40 ); System.out.println( " _41 = " + _41 ); System.out.println( " _42 = " + _42 ); System.out.println( " _43 = " + _43 ); System.out.println( " _44 = " + _44 ); System.out.println( " _45 = " + _45 ); System.out.println( " _46 = " + _46 ); System.out.println( " _47 = " + _47 ); System.out.println( " _48 = " + _48 ); System.out.println( " _49 = " + _49 ); System.out.println( " _50 = " + _50 ); System.out.println( " _51 = " + _51 ); System.out.println( " _52 = " + _52 ); System.out.println( " _53 = " + _53 ); System.out.println( " _54 = " + _54 ); System.out.println( " _55 = " + _55 ); System.out.println( " _56 = " + _56 ); System.out.println( " _57 = " + _57 ); System.out.println( " _58 = " + _58 ); System.out.println( " _59 = " + _59 ); System.out.println( " _60 = " + _60 ); System.out.println( " _61 = " + _61 ); System.out.println( " _62 = " + _62 ); System.out.println( " _63 = " + _63 ); System.out.println( " _64 = " + _64 ); 

Answer 5

如果整数加法溢出，那么结果是math和的低位，如用一些足够大的二进制补码格式表示的。 如果发生溢出，则结果的符号与两个操作数值的math和的符号不同。

http://java.sun.com/docs/books/jls/second_edition/html/expressions.doc.html#13510

Answer 6

这是一个解决scheme的答案，所以你仍然可以继续基本上无限。 我推荐一个if（int> nearmax）然后传递给新的int例如：

 int x = 2000000000; x++; int stacker = 0; if (x > 2000000000) { int temp = x; x = temp - 2000000000 stacker++; } 

那么你也可以在必要时拆散

说x = 0

 x--; if (x < 0 && stacker > 0) { int temp = x; x = 2000000000 + temp;//plus because it's negative stacker--; } 

这给了2000000000 x 2000000000，我的意思是…你可以继续这样做，所以…亚…

当然，如果你想使用负数，你可以走得更远