这个在java里怎么实现

[别以为你站在珠峰就能看到全世界]

sprintf(str, "%0.*f", n, 3.123456789); n是参数，会自动代替*号，可以动态控制输出小数点后面的位数。

java里面怎么实现类似的功能，String的format不支持

[李德胜1995]

sprintf是C语言的吧？？？这是要干嘛？？？简单控制小数点的位数而已？？

[脱落叶子]

使用DecimalFormat类进行对十进制的数进行格式输出 double b = 10.0 / 3.0; //5位小数输出 DecimalFormat df = new DecimalFormat("0.0000"); System.out.println(df.format(b));

[kingbaron]

写了一个简单版本的demo：

package simple.demo;

import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.FieldPosition;

/**
 * Created  on 2017/12/2.
 *
 * @author kingbaron
 */
public class FormatDemo {
    public static void main(String[] args) {
        numberFormatTest();
    }

    public static void numberFormatTest() {
        NumberFormatHelper numberFormatHelper=new NumberFormatHelper();
        System.out.println(numberFormatHelper.numberFormat(5244.1314,1,5));
        System.out.println(numberFormatHelper.numberFormat("5244.1314",1,1));
        System.out.println(numberFormatHelper.numberFormat(5244.1314));
        System.out.println(numberFormatHelper.numberFormat("5244E1"));
    }

    static class NumberFormatHelper{
        public String numberFormat(Object obj){
            if(obj==null) {return "";}
            return String.valueOf(new BigDecimal(obj.toString()));
        }

        public String numberFormat(Object obj,int integer,int precision){
            if(obj==null) {return "";}
            return this.decimalFormat(new BigDecimal(obj.toString()),integer,precision);
        }
        /**
         * BigDecimal类型数字格式化字符串输出
         * @param num  待格式化数字
         * @param integer 整数部分精度
         * @param precision 小数部分精度
         * @return
         */
        public String decimalFormat(BigDecimal num,int integer,int precision){
            StringBuilder stringBuilder=new StringBuilder();
            while(integer-->0){
                stringBuilder.append('0');
            }
            if(precision>0){
                stringBuilder.append('.');
                while(precision-->0){
                    stringBuilder.append('0');
                }
            }
            DecimalFormat decimalFormat=new DecimalFormat(stringBuilder.toString());
            return decimalFormat.format(num,new StringBuffer(),new FieldPosition(5)).toString();
        }
    }
}

[kingbaron]

有点不干净上面的例子，修改了一下

package simple.demo;

import java.math.BigDecimal;
import java.text.DecimalFormat;

/**
 * Created  on 2017/12/2.
 *
 * @author kingbaron
 */
public class FormatDemo {
    public static void main(String[] args) {
        numberFormatTest();
    }

    public static void numberFormatTest() {
        NumberFormatHelper numberFormatHelper=new NumberFormatHelper();
        System.out.println(numberFormatHelper.numberFormat(5244.1314,1,5));
        System.out.println(numberFormatHelper.numberFormat("5244.1314",1,1));
        System.out.println(numberFormatHelper.numberFormat(5244.1314));
        System.out.println(numberFormatHelper.numberFormat("5244E1"));
    }

    static class NumberFormatHelper{
        public String numberFormat(Object obj){
            if(obj==null) {return "";}
            return String.valueOf(new BigDecimal(obj.toString()));
        }

        public String numberFormat(Object obj,int integer,int precision){
            if(obj==null) {return "";}
            return this.decimalFormat(new BigDecimal(obj.toString()),integer,precision);
        }
        /**
         * BigDecimal类型数字格式化字符串输出
         * @param num  待格式化数字
         * @param integer 整数部分精度
         * @param precision 小数部分精度
         * @return
         */
        public String decimalFormat(BigDecimal num,int integer,int precision){
            StringBuilder stringBuilder=new StringBuilder();
            while(integer-->0){
                stringBuilder.append('0');
            }
            if(precision>0){
                stringBuilder.append('.');
                while(precision-->0){
                    stringBuilder.append('0');
                }
            }
            DecimalFormat decimalFormat=new DecimalFormat(stringBuilder.toString());
            return decimalFormat.format(num);
        }
    }
}