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public class Test{
    public static void main(String args[]){
        System.out.println(0.05+0.01);
        System.out.println(1.0-0.42);
        System.out.println(4.015*100);
        System.out.println(123.3/100);
    }
};
ÄãûÓп´´í£¡½á¹ûȷʵÊÇ
0.060000000000000005
0.5800000000000001
401.49999999999994
1.2329999999999999
JavaÖеļòµ¥¸¡µãÊýÀàÐÍfloatºÍdouble²»Äܹ»½øÐÐÔËËã¡£²»¹âÊÇJava£¬ÔÚÆäËüºÜ¶à±à³ÌÓïÑÔÖÐÒ²ÓÐÕâÑùµÄÎÊÌâ¡£ÔÚ´ó¶àÊýÇé¿öÏ£¬¼ÆËãµÄ½á¹ûÊÇ׼ȷµÄ£¬µ«ÊǶàÊÔ¼¸´Î£¨¿ÉÒÔ×öÒ»¸öÑ­»·£©¾Í¿ÉÒÔÊÔ³öÀàËÆÉÏÃæµÄ´íÎó¡£ÏÖÔÚÖÕÓÚÀí½âΪʲôҪÓÐBCDÂëÁË¡£
Õâ¸öÎÊÌâÏ൱ÑÏÖØ£¬Èç¹ûÄãÓÐ9.999999999999Ôª£¬ÄãµÄ¼ÆËã»úÊDz»»áÈÏΪÄã¿ÉÒÔ¹ºÂò10ÔªµÄÉÌÆ·µÄ¡£
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public double round(double value){
    return Math.round(value*100)/100.0;
}
·Ç³£²»ÐÒ£¬ÉÏÃæµÄ´úÂë²¢²»ÄÜÕý³£¹¤×÷£¬¸øÕâ¸ö·½·¨´«Èë4.015Ëü½«·µ»Ø4.01¶ø²»ÊÇ4.02£¬ÈçÎÒÃÇÔÚÉÏÃæ¿´µ½µÄ
4.015*100=401.49999999999994
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java.text.DecimalFormatÒ²²»Äܽâ¾öÕâ¸öÎÊÌ⣺
System.out.println(new java.text.DecimalFormat("0.00").format(4.025));
Êä³öÊÇ4.02
 
BigDecimal
ÔÚ¡¶Effective Java¡·Õâ±¾ÊéÖÐÒ²Ìáµ½Õâ¸öÔ­Ôò£¬floatºÍdoubleÖ»ÄÜÓÃÀ´×ö¿ÆÑ§¼ÆËã»òÕßÊǹ¤³Ì¼ÆË㣬ÔÚÉÌÒµ¼ÆËãÖÐÎÒÃÇÒªÓÃjava.math.BigDecimal¡£BigDecimalÒ»¹²ÓÐ4¸ö¹»Ôì·½·¨£¬ÎÒÃDz»¹ØÐÄÓÃBigIntegerÀ´¹»ÔìµÄÄÇÁ½¸ö£¬ÄÇô»¹ÓÐÁ½¸ö£¬ËüÃÇÊÇ£º
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public List queryAll(int fcateId) {
List list = new ArrayList();
String sql = "select * from g_Account where fCateID=? order by fCode";
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