数字格式化

double a = 3123456.23;

double b = 0.23;

 DecimalFormat df = new DecimalFormat("##,#00.00");

System.out.println(df.format(a));                 //输出结果：3,123,456.23

df.applyPattern("##.##%");

System.out.println(df.format(b));                 //输出结果：23%