您需要使用Formatter，下面的代码使用NumberFormat

    int inputNo = 1;
    NumberFormat nf = NumberFormat.getInstance();
    nf.setMaximumIntegerDigits(4);
    nf.setMinimumIntegerDigits(4);
    nf.setGroupingUsed(false);

    System.out.println("Formatted Integer : " + nf.format(inputNo));

输出:0001

试试这个:

import java.text.DecimalFormat; 

DecimalFormat df = new DecimalFormat("0000");

String c = df.format(9);   // Output: 0009

String a = df.format(99);  // Output: 0099

String b = df.format(999); // Output: 0999

下面是另一种将整数左侧填充为0的方法。您可以根据您的方便增加零的数量。已添加一个检查，以返回与配置的负数或大于或等于零的值相同的值。你可以根据你的要求进一步修改。

/**
 * 
 * @author Dinesh.Lomte
 *
 */
public class AddLeadingZerosToNum {
    
    /**
     * 
     * @param args
     */
    public static void main(String[] args) {
        
        System.out.println(getLeadingZerosToNum(0));
        System.out.println(getLeadingZerosToNum(7));
        System.out.println(getLeadingZerosToNum(13));
        System.out.println(getLeadingZerosToNum(713));
        System.out.println(getLeadingZerosToNum(7013));
        System.out.println(getLeadingZerosToNum(9999));
    }
    /**
     * 
     * @param num
     * @return
     */
    private static String getLeadingZerosToNum(int num) {
        // Initializing the string of zeros with required size
        String zeros = new String("0000");
        // Validating if num value is less then zero or if the length of number 
        // is greater then zeros configured to return the num value as is
        if (num < 0 || String.valueOf(num).length() >= zeros.length()) {
            return String.valueOf(num);
        }
        // Returning zeros in case if value is zero.
        if (num == 0) {
            return zeros;
        }
        return new StringBuilder(zeros.substring(0, zeros.length() - 
                String.valueOf(num).length())).append(
                        String.valueOf(num)).toString();
    }
}

输入

0

7

13

713

7013

9999

输出

0000

0007

0013

7013

9999

您需要使用Formatter，下面的代码使用NumberFormat

    int inputNo = 1;
    NumberFormat nf = NumberFormat.getInstance();
    nf.setMaximumIntegerDigits(4);
    nf.setMinimumIntegerDigits(4);
    nf.setGroupingUsed(false);

    System.out.println("Formatted Integer : " + nf.format(inputNo));

输出:0001

你可以用谷歌番石榴:

Maven:

<dependency>
     <artifactId>guava</artifactId>
     <groupId>com.google.guava</groupId>
     <version>14.0.1</version>
</dependency>

示例代码:

String paddedString1 = Strings.padStart("7", 3, '0'); //"007"
String paddedString2 = Strings.padStart("2020", 3, '0'); //"2020"

注意:

Guava是一个非常有用的库，它还提供了许多与集合、缓存、函数习语、并发、字符串、原语、范围、IO、哈希、EventBus等相关的特性

裁判:GuavaExplained

Kotlin的

fun Calendar.getFullDate(): String {
    val mYear = "${this.get(Calendar.YEAR)}-"
    val mMonth = if (this.get(Calendar.MONTH) + 1 < 10) {
        "0${this.get(Calendar.MONTH) + 1}-"
    } else {
        "${this.get(Calendar.MONTH)+ 1}-"
    }
    val mDate = if (this.get(Calendar.DAY_OF_MONTH)  < 10) {
        "0${this.get(Calendar.DAY_OF_MONTH)}"
    } else {
        "${this.get(Calendar.DAY_OF_MONTH)}"
    }
    return mYear + mMonth + mDate
}

并将其用作

val date: String = calendar.getFullDate()