Java中double保留兩位小數(shù)的多種方法

更新時(shí)間：2023年07月05日 15:32:17 作者：小白蹦蹦跳跳

這篇文章主要給大家介紹了關(guān)于Java中double保留兩位小數(shù)的多種方法,對(duì)于double數(shù)據(jù)類型進(jìn)行計(jì)算發(fā)生的精度丟失的情況,可以按照自己的需求選擇任意方式,需要的朋友可以參考下

方法一：格式化輸出

double one=5;
System.out.printf("%.02f", one);  //5.00

方法二：BigDecimal.setScale()

BigDecimal.setScale()這個(gè)方法是用于格式化小數(shù)點(diǎn)

setScale(0)表示保留整數(shù)
setScale(1)表示保留一位小數(shù)，默認(rèn)用四舍五入
setScale(1,BigDecimal.ROUND_DOWN)直接刪除多余的小數(shù)位，如2.35會(huì)變成2.3
setScale(1,BigDecimal.ROUND_UP)進(jìn)位處理，2.35變成2.4
setScale(1,BigDecimal.ROUND_HALF_UP)四舍五入，2.35變成2.4
setScale(1,BigDecimal.ROUND_HALF_DOWN)四舍五入，2.35變成2.3，如果是5則向下舍
BigDecimal num1 = new BigDecimal(2.225667); //這種寫法不允許，會(huì)造成精度損失
BigDecimal num = new BigDecimal(“2.225667”); //一般都會(huì)這樣寫最好

double one1 = 5.459;
BigDecimal two1 = new BigDecimal(one1);
double three1 = two1.setScale(2,BigDecimal.ROUND_HALF_UP).doubleValue();
System.out.println(three1);  //5.46

方法三：DecimalFormat

double one2 = 5.459;
DecimalFormat format2 = new DecimalFormat("#.00");
String str2 = format2.format(one2);
System.out.println(str2);  //5.46
double four2 = Double.parseDouble(str2);
System.out.println(four2);  //5.46

方法四：String.format

double one3 = 5.459;
String  str3 = String.format("%.2f",one3);
System.out.println(str3);  //5.46
double four3 = Double.parseDouble(str3);
System.out.println(four3);  //5.46

方法五：NumberFormat

double one4 = 5.459;
NumberFormat format4 = NumberFormat.getInstance();
format4.setMaximumFractionDigits(2);
String  str4 = format4.format(one4);
System.out.println(str4);  //5.46
double two4 = Double.parseDouble(str4);
System.out.println(two4);  //5.46

補(bǔ)充：

Double.valueOf(String s)返回保存用參數(shù)字符串s表示的double值的Double對(duì)象
Double.parseDouble返回一個(gè)初始化為指定String表示的值的新double
如果要變成int,則用Integer.parseInt()==

方法二到四遇到的問題：

不能將double 5轉(zhuǎn)換成double 5.00輸出

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

public class test1 {
    public static void main(String[] args) {

        double one1 = 5;
        BigDecimal two1 = new BigDecimal(one1);
        double three1 = two1.setScale(2,BigDecimal.ROUND_HALF_UP).doubleValue();
        System.out.println(three1);  //5.0

        double one2 = 5;
        DecimalFormat format2 = new DecimalFormat("#.00");
        String str2 = format2.format(one2);
        System.out.println(str2);  //5.00
        double four2 = Double.parseDouble(str2);
        System.out.println(four2);  //5.0

        double one3 = 5;
        String  str3 = String.format("%.2f",one3);
        System.out.println(str3);  //5.00
        double four3 = Double.parseDouble(str3);
        System.out.println(four3);  //5.0

        double one4 = 5;
        NumberFormat format4 = NumberFormat.getInstance();
        format4.setMaximumFractionDigits(2);
        String  str4 = format4.format(one4);
        System.out.println(str4);  //5
        double two4 = Double.parseDouble(str4);
        System.out.println(two4);  //5.0
    }
}

package code;

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

public class test1 {
    public static void main(String[] args) {

        double one1 = 5.0;
        BigDecimal two1 = new BigDecimal(one1);
        double three1 = two1.setScale(2,BigDecimal.ROUND_HALF_UP).doubleValue();
        System.out.println(three1);  //5.0

        double one2 = 5.0;
        DecimalFormat format2 = new DecimalFormat("#.00");
        String str2 = format2.format(one2);
        System.out.println(str2);  //5.00
        double four2 = Double.parseDouble(str2);
        System.out.println(four2);  //5.0

        double one3 = 5.0;
        String  str3 = String.format("%.2f",one3);
        System.out.println(str3);  //5.00
        double four3 = Double.parseDouble(str3);
        System.out.println(four3);  //5.0

        double one4 = 5.0;
        NumberFormat format4 = NumberFormat.getInstance();
        format4.setMaximumFractionDigits(2);
        String  str4 = format4.format(one4);
        System.out.println(str4);  //5
        double two4 = Double.parseDouble(str4);
        System.out.println(two4);  //5.0
    }
}

package code;

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

public class test1 {
    public static void main(String[] args) {

        double one1 = 5.00;
        BigDecimal two1 = new BigDecimal(one1);
        double three1 = two1.setScale(2,BigDecimal.ROUND_HALF_UP).doubleValue();
        System.out.println(three1);  //5.0
        
        double one2 = 5.00;
        DecimalFormat format2 = new DecimalFormat("#.00");
        String str2 = format2.format(one2);
        System.out.println(str2);  //5.00
        double four2 = Double.parseDouble(str2);
        System.out.println(four2);  //5.0

        double one3 = 5.00;
        String  str3 = String.format("%.2f",one3);
        System.out.println(str3);  //5.00
        double four3 = Double.parseDouble(str3);
        System.out.println(four3);  //5.0

        double one4 = 5.00;
        NumberFormat format4 = NumberFormat.getInstance();
        format4.setMaximumFractionDigits(2);
        String  str4 = format4.format(one4);
        System.out.println(str4);  //5
        double two4 = Double.parseDouble(str4);
        System.out.println(two4);  //5.0
    }
}

不管是5或者是5.000…最后的結(jié)果都是5.0