部分内容转自:java 彻底理解 byte char short int float long double
首先说byte:
这段是摘自jdk中 Byte.java中的源代码:
1 /** 2 * A constant holding the minimum value a <code>byte</code> can 3 * have, -2<sup>7</sup>. 4 */ 5 public static final byte MIN_VALUE = -128; 6 7 /** 8 * A constant holding the maximum value a <code>byte</code> can 9 * have, 2<sup>7</sup>-1. 10 */ 11 public static final byte MAX_VALUE = 127;
从这里可以看出 byte的取值范围:-128 --- 127;
从计算机组成原理的角度可以解释:byte在计算机中是占8个字节的 而且byte 是有符号整形 用二进制表示时候最高位为符号位 0代表正数 1代表负数。
最大值:127 0111 1111 即2的7次方减去1;
最小值:-128 这个数字曾经困扰我很久, 要知道正数在计算机中是以原码形式存在的,负数在计算机中是以其补码形式存在的,那么一个负数的补码是怎么计算的呢? 就是负数的绝对值的原码转为二进制再按位取反后加1,
下边这个10和-10为例来介绍的 :10原码:0000 1010 它在计算机中的存储就是 0000 1010, 那么-10呢? 按照前面说的 算除其绝对值为10,转为二进制 0000 1010 按位取反 1111 0101 再加1后:1111 0110,此为-10补码 ,好的,计算机中的1111 0110就是代表-10了。
我们来看 -128 绝对值128的二进制表示:1000 0000 按位取反 0111 1111 加1后:1000 0000,也就是说 -128在计算机中的表示就是 1000 0000 了, 再来看一下-129 在计算机中的表示,绝对值129的范围已经超出了了byte的位数。
再有还可以通过
1 System.out.println(Byte.MAX_VALUE); //最大值 2 System.out.println(Byte.MIN_VALUE); //最小值
输出Byte的最大值和最小值。
综上所述 byte的取值范围只能是:-128 -- 127了 即 负的2的7次方到2的7次方减去1。
相应的 short 作为16位有符号整形,int作为32位有符号整形, long 作为64位有符号整形 都可以如上计算出 取值范围
Short:
Unicode Character Representations
The char
data type (and therefore the value that a Character
object encapsulates) are based on the original Unicode specification, which defined characters as fixed-width 16-bit entities. The Unicode Standard has since been changed to allow for characters whose representation requires more than 16 bits. The range of legal code points is now U+0000 to U+10FFFF, known as Unicode scalar value.
Character.java中的源代码:
/** * The constant value of this field is the smallest value of type * <code>char</code>, <code>‘/u0000‘</code>. * * @since 1.0.2 */ public static final char MIN_VALUE = ‘/u0000‘; /** * The constant value of this field is the largest value of type * <code>char</code>, <code>‘/uFFFF‘</code>. * * @since 1.0.2 */ public static final char MAX_VALUE = ‘/uffff‘;
Long:
float作为32位的浮点型:
摘自Float.java源码:
/** * A constant holding the largest positive finite value of type * <code>float</code>, (2-2<sup>-23</sup>)·2<sup>127</sup>. * It is equal to the hexadecimal floating-point literal * <code>0x1.fffffeP+127f</code> and also equal to * <code>Float.intBitsToFloat(0x7f7fffff)</code>. */ public static final float MAX_VALUE = 3.4028235e+38f; // 0x1.fffffeP+127f /** * A constant holding the smallest positive nonzero value of type * <code>float</code>, 2<sup>-149</sup>. It is equal to the * hexadecimal floating-point literal <code>0x0.000002P-126f</code> * and also equal to <code>Float.intBitsToFloat(0x1)</code>. */ public static final float MIN_VALUE = 1.4e-45f; // 0x0.000002P-126f
double 作为64为浮点型
Double.java源码:
1 /** 2 * A constant holding the largest positive finite value of type 3 * <code>double</code>, 4 * (2-2<sup>-52</sup>)·2<sup>1023</sup>. It is equal to 5 * the hexadecimal floating-point literal 6 * <code>0x1.fffffffffffffP+1023</code> and also equal to 7 * <code>Double.longBitsToDouble(0x7fefffffffffffffL)</code>. 8 */ 9 public static final double MAX_VALUE = 1.7976931348623157e+308; // 0x1.fffffffffffffP+1023 10 11 /** 12 * A constant holding the smallest positive nonzero value of type 13 * <code>double</code>, 2<sup>-1074</sup>. It is equal to the 14 * hexadecimal floating-point literal 15 * <code>0x0.0000000000001P-1022</code> and also equal to 16 * <code>Double.longBitsToDouble(0x1L)</code>. 17 */ 18 public static final double MIN_VALUE = 4.9e-324; // 0x0.0000000000001P-1022