货币格式化
double 格式化输出保留两位小数
DecimalFormat
Note: 由于"四舍六入五取偶" 规则, 只能用第一种方法
# Decimal formats are generally not synchronized
new DecimalFormat("#0.00").format(0.00) // 0.00
new DecimalFormat("#0.00").format(0.1388) // 0.14
String.format
普通格式化,不能用于货币表示
String.format("%.2f", 0.00) // 0.00
String.format("%.2f", -0.00) // -0.00
String.format("%.2f", 0.439) // 0.44
benchmark
@Test
public void benchmark() {
int times = 1000000;
double[] samples = new double[]{0.00, -0.00, 0.00012, 9999999.8888999e7};
String[] res = new String[]{"0.00", "-0.00", "0.00", "99999998888999.00"};
StopWatch stopWatch = new StopWatch();
stopWatch.start();
for (int i = 0; i < times; ++i) {
for (int j = 0; j < samples.length; ++ j) {
DecimalFormat df = new DecimalFormat("#0.00");
Assert.assertEquals(res[j], df.format(samples[j]));
}
}
stopWatch.split();
System.out.println(stopWatch.getSplitTime());
stopWatch.reset();
stopWatch.start();
for (int i = 0; i < times; ++i) {
for (int j = 0; j < samples.length; ++ j) {
Assert.assertEquals(res[j], String.format("%.2f", samples[j]));
}
}
stopWatch.split();
System.out.println(stopWatch.getSplitTime());
stopWatch.stop();
}