Two methods have been used: DecimalFormat and Math.round().
usage:
1、DecimalFormat：（String java.text.NumberFormat.format(double number)方法）
float f = 0.5555f;
DecimalFormat df1 = new DecimalFormat(" #.00 "); //Reserve two decimal places, if it is a few tenths, the 0 before the decimal point will not be displayed, and the number of zeros after the decimal point will be reserved
df1.format(f);
#Indicates that if the bit is 0, it does not need to be displayed, and 0 means that if the bit is 0, it is still displayed;
The definition of the function is: ;
Therefore, the parameter passed is double, and float (implicit conversion) can also be passed, and the final result is String type.
2、Math.round()：（int java.lang.Math.round(float a)方法）
float f = 1.222f;
f = Math.round(f * 100 ) / 100 f; //multiply by 100, then divide by 100 to convert to floating point type
/** Keep as many decimal places as you multiply
**Note that the Math.round() method passes the float type!
*/
Both methods round off.
If it is a floating-point type, it is recommended to use the Math.round method, or you can DIY code according to your needs.
For a detailed explanation, please see the code comments and console output: (including the format of decimalFloat and the implementation logic of the Math.round function)
package testMap;
import java.text.DecimalFormat;
public class TestFloat {
public static void main(String[] args) {
// TODO Auto-generated method stub
//四舍五入保留两位
float f = 0.5555f;
//decimalFormat是将double类型数据转换为字符串，并进行格式化
//#表示这位如果是0则不必显示出来，0则表示这位如果是
//format函数：String java.text.NumberFormat.format(double number)
DecimalFormat df1 = new DecimalFormat("#.00");//首位0不显示出来，即0.1显示为 .1
DecimalFormat df2 = new DecimalFormat("0.00");//首位0显示出来，即0.1显示为 0.1
System.out.println("--------DecimalFormat----------");
System.out.println("df1==" + df1.format(f));
System.out.println("df2==" + df2.format(f));
System.out.println(df1.format(f).getClass());//String类型
System.out.println(Float.parseFloat(df1.format(f)));//转换为float类型
System.out.println(String.valueOf(df1.format(f)));
// System.out.println(Float.toString(df1.format(f)));//转换为String类型
f = 0.595f;
//Math.round()方法是将浮点类型数据 乘以10的多少次方 ，取整，然后 + 0.5 除以10的多少次方，取小数点后多少位
// 如乘以1000 则取小数点后3位
System.out.println("---------Math.round()----------");
System.out.println(Math.round(f * 100) / 100f);//四舍五入后如果末尾是0，自动省略，不显示
// System.out.println(df1.format("1.2"));//参数必须是数值型String java.text.NumberFormat.format(double number)
System.out.println(Float.toString(f));//转换为String输出效果
System.out.println(Float.toString(f));//转换为String输出效果
System.out.println("-----------Math.round()的正数非特殊值实现逻辑--------------");
f = 11.115111f;
int b = (int) (f * 100 + 0.5);
float a = b / 100f;
System.out.println("a==" + a);
System.out.println((int)(f * 100 + 0.5) / 100f);
f = -12.115f;
System.out.println("负数" + Math.round(f * 100) / 100f);
f = -12.116f;
System.out.println("负数" + Math.round(f * 100) / 100f);
System.out.println("-------Math.round()的负数非特殊值实现逻辑--------");
int c = (int) (f * 100 - 0.5);
float d = c / 100f;
System.out.println("d==" + d);
System.out.println((int)(d * 100 - 0.5) / 100f);
}
}
Console output:
Screenshot below:
----The following is the console output-----(same as above, afraid of losing the picture)
--------DecimalFormat----------
df1==.56
df2==0.56
class java.lang.String
0.56
.56
---------Math.round( )----------
0.6
0.595
0.595
-----------Math.round() positive non-special value implementation logic ------------ --
a==11.12
11.12
Negative Number-12.11
Negative Number-12.12
-------Math.round()'s negative non-special value implementation logic --------
d==-12.12
-12.12
By the way, paste the code of NumberFormat.format():
/**
* Specialization of format.
*
* @param number the double number to format
* @return the formatted String
* @exception ArithmeticException if rounding is needed with rounding
* mode being set to RoundingMode.UNNECESSARY
* @see java.text.Format#format
*/
public final String format(double number) {
// Use fast-path for double result if that works
String result = fastFormat(number);
if (result != null)
return result;
return format(number, new StringBuffer(),
DontCareFieldPosition.INSTANCE).toString();
}