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J2SE 5.0实例---静态引入
摘要: J2SE 5.0实例---静态引入
静态引入（static import）
在过去我们要使用其他包中某类的静态变量，一般都要在前面加上对应的类名：
<table class="MsoTableGrid" style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: silver; MARGIN: auto auto auto 59.4pt; BORDER-LEFT: medium none; WIDTH: 378pt; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt; mso-yfti-tbllook: 480; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext" cellspacing="0" cellpadding="0" width="504" border="1"><tr style="mso-yfti-irow: 0; mso-yfti-lastrow: yes"><td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1pt solid; WIDTH: 378pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BACKGROUND-COLOR: transparent; mso-border-alt: solid windowtext .5pt" valign="top" width="504">double r = Math.cos(Math.PI * theta);
</td></tr></table>使用静态引入，我们可以把前面的类名去掉，静态引入的语句是这样的：
<table class="MsoTableGrid" style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: silver; MARGIN: auto auto auto 59.4pt; BORDER-LEFT: medium none; WIDTH: 378pt; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt; mso-yfti-tbllook: 480; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext" cellspacing="0" cellpadding="0" width="504" border="1"><tr style="mso-yfti-irow: 0; mso-yfti-lastrow: yes"><td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1pt solid; WIDTH: 378pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BACKGROUND-COLOR: transparent; mso-border-alt: solid windowtext .5pt" valign="top" width="504">import static java.lang.Math.PI;
</td></tr></table>必须注意到这里最后不是到类Math,而是直接到了定义的变量PI。
静态引入不只对静态变量，也可以针对静态方法。此外还可以使用*，如下面所示：
<table class="MsoTableGrid" style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: silver; MARGIN: auto auto auto 59.4pt; BORDER-LEFT: medium none; WIDTH: 378pt; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt; mso-yfti-tbllook: 480; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext" cellspacing="0" cellpadding="0" width="504" border="1"><tr style="mso-yfti-irow: 0; mso-yfti-lastrow: yes"><td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 1pt solid; WIDTH: 378pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BACKGROUND-COLOR: transparent; mso-border-alt: solid windowtext .5pt" valign="top" width="504">import static java.lang.Math.*;
</td></tr></table>除非我们对某个静态常量（或者方法）访问频度很大，否则应该尽量避免使用静态引入。
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