保留小數點1位 且舍掉後面所有

import java.math.RoundingMode;
import java.text.DecimalFormat;
public class Main {
    public static void main(String[] args) {
            DecimalFormat df = new DecimalFormat("0.0");
        double num = 11.286;
//        DecimalFormat df = new DecimalFormat("#.##");
        //指定RoundingMode
 

        df.setRoundingMode(RoundingMode.DOWN);
        String str = df.format(num);
        double formatNum = Double.parseDouble(str);
        System.out.println(formatNum);
    }
}

保留小數點1位 四捨五入

import java.math.RoundingMode;
import java.text.DecimalFormat;
public class Main {
    public static void
 
 main(String[] args) {
            DecimalFormat df = new DecimalFormat("0.0");
        double num = 11.286;
//        DecimalFormat df = new DecimalFormat("#.##");
        //指定RoundingMode
        df.setRoundingMode(RoundingMode.DOWN);
        String str = df.format(num);
        double formatNum = Double.parseDouble(str);
        System.out.println(formatNum);
    }
}
 

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