如何用左零填充一个整数?

How do you left pad an int with zeros when converting to a String in java?

在java中，当转换为字符串时，如何用0填充int ?

I'm basically looking to pad out integers up to 9999 with leading zeros (e.g. 1 = 0001).

我基本上是想用前导0填充到9999的整数(例如，1 = 0001)。

13 个解决方案

#1

Use java.lang.String.format(String,Object...) like this:

使用java.lang.String.format(字符串、对象…)是这样的:

String.format("%05d", yournumber);

for zero-padding with a length of 5. For hexadecimal output replace the d with an x as in "%05x".

用于长度为5的零填充。对于十六进制输出，用“%05x”中的x替换d。

The full formatting options are documented as part of java.util.Formatter.

完整的格式化选项作为java.util.Formatter的一部分进行了文档化。

#2

If you for any reason use pre 1.5 Java then may try with Apache Commons Lang method

如果您出于某种原因使用pre - 1.5 Java，那么可以尝试使用Apache Commons Lang方法

org.apache.commons.lang.StringUtils.leftPad(String str, int size, '0')

#3

Let's say you want to print 11 as 011

假设你想打印11。

You could use a formatter: "%03d".

您可以使用格式化程序:“%03d”。

You can use this formatter like this:

你可以使用这样的格式化程序:

int a = 11;
String with3digits = String.format("%03d", a);
System.out.println(with3digits);

Alternatively, some java methods directly support these formatters:

或者，一些java方法直接支持这些格式器:

System.out.printf("%03d", a);

#4

Found this example... Will test...

发现这个例子…将测试……

import java.text.DecimalFormat;
class TestingAndQualityAssuranceDepartment
{
    public static void main(String [] args)
    {
        int x=1;
        DecimalFormat df = new DecimalFormat("00");
        System.out.println(df.format(x));
    }
}

Tested this and:

测试这个:

String.format("%05d",number);

Both work, for my purposes I think String.Format is better and more succinct.

这两种都可以，就我而言，我认为是弦。格式更好更简洁。

#5

If performance is important in your case you could do it yourself with less overhead compared to the String.format function:

如果性能在您的情况中是重要的，那么您可以自己使用比字符串更少的开销。格式功能:

/**
 * @param in The integer value
 * @param fill The number of digits to fill
 * @return The given value left padded with the given number of digits
 */
public static String lPadZero(int in, int fill){

    boolean negative = false;
    int value, len = 0;

    if(in >= 0){
        value = in;
    } else {
        negative = true;
        value = - in;
        in = - in;
        len ++;
    }

    if(value == 0){
        len = 1;
    } else{         
        for(; value != 0; len ++){
            value /= 10;
        }
    }

    StringBuilder sb = new StringBuilder();

    if(negative){
        sb.append('-');
    }

    for(int i = fill; i > len; i--){
        sb.append('0');
    }

    sb.append(in);

    return sb.toString();       
}

Performance

性能

public static void main(String[] args) {
    Random rdm;
    long start; 

    // Using own function
    rdm = new Random(0);
    start = System.nanoTime();

    for(int i = 10000000; i != 0; i--){
        lPadZero(rdm.nextInt(20000) - 10000, 4);
    }
    System.out.println("Own function: " + ((System.nanoTime() - start) / 1000000) + "ms");

    // Using String.format
    rdm = new Random(0);        
    start = System.nanoTime();

    for(int i = 10000000; i != 0; i--){
        String.format("%04d", rdm.nextInt(20000) - 10000);
    }
    System.out.println("String.format: " + ((System.nanoTime() - start) / 1000000) + "ms");
}

Result

结果

Own function: 1697ms

的功能:1697 ms

String.format: 38134ms

字符串。格式:38134毫秒

#6

You can use Google Guava:

你可以使用谷歌番石榴:

Maven:

Maven:

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

Sample code:

示例代码:

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

Note:

注意:

Guava is very useful library, it also provides lots of features which related to Collections, Caches, Functional idioms, Concurrency, Strings, Primitives, Ranges, IO, Hashing, EventBus, etc

番石榴是一个非常有用的库，它还提供了许多与集合、缓存、功能习语、并发性、字符串、原语、范围、IO、散列、EventBus等相关的特性

Ref: GuavaExplained

裁判:GuavaExplained

#7

Although many of the above approaches are good, but sometimes we need to format integers as well as floats. We can use this, particularly when we need to pad particular number of zeroes on left as well as right of decimal numbers.

虽然上面的许多方法都很好，但是有时我们需要格式化整数和浮点数。我们可以使用这个，特别是当我们需要在左和右的小数上加上一个特定的0的时候。

import java.text.NumberFormat;  
public class NumberFormatMain {  

public static void main(String[] args) {  
    int intNumber = 25;  
    float floatNumber = 25.546f;  
    NumberFormat format=NumberFormat.getInstance();  
    format.setMaximumIntegerDigits(6);  
    format.setMaximumFractionDigits(6);  
    format.setMinimumFractionDigits(6);  
    format.setMinimumIntegerDigits(6);  

    System.out.println("Formatted Integer : "+format.format(intNumber).replace(",",""));  
    System.out.println("Formatted Float   : "+format.format(floatNumber).replace(",",""));  
 }    
}  

#8

int x = 1;
System.out.format("%05d",x);

if you want to print the formatted text directly onto the screen.

如果您想将格式化后的文本直接打印到屏幕上。

#9

Try this one:

试试这个:

DecimalFormat df = new DecimalFormat("0000");
String c = df.format(9);   // 0009
String a = df.format(99);  // 0099
String b = df.format(999); // 0999

#10

Check my code that will work for integer and String.

检查我的用于整数和字符串的代码。

Assume our first number is 2. And we want to add zeros to that so the the length of final string will be 4. For that you can use following code

假设第一个数是2。我们想把0加进去最终的弦的长度是4。为此，您可以使用以下代码

    int number=2;
    int requiredLengthAfterPadding=4;
    String resultString=Integer.toString(number);
    int inputStringLengh=resultString.length();
    int diff=requiredLengthAfterPadding-inputStringLengh;
    if(inputStringLengh<requiredLengthAfterPadding)
    {
        resultString=new String(new char[diff]).replace("\0", "0")+number;
    }        
    System.out.println(resultString);

#11

You need to use a Formatter, following code uses NumberFormat

您需要使用格式化程序，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));

Output: 0001

输出:0001

#12

public static String zeroPad(long number, int width) {
   long wrapAt = (long)Math.pow(10, width);
   return String.valueOf(number % wrapAt + wrapAt).substring(1);
}

The only problem with this approach is that it makes you put on your thinking hat to figure out how it works.

这种方法的唯一问题是，它会让你戴上思考的帽子，弄清楚它是如何工作的。

#13

No packages needed:

不需要包:

String paddedString = i < 100 ? i < 10 ? "00" + i : "0" + i : "" + i;

This will pad the string to three characters, and it is easy to add a part more for four or five. I know this is not the perfect solution in any way (especially if you want a large padded string), but I like it.

这将把字符串填充为3个字符，并且很容易为4或5添加更多的部分。我知道这不是一个完美的解决方案(尤其是如果你想要一个大的填充字符串)，但我喜欢它。