有没有一种简单的方法在Java中填充字符串?
这似乎是一些类似于StringUtil的API应该有的东西,但我找不到任何可以实现这一点的内容。
Java一行代码,不使用花哨的库。
// 6 characters padding example
String pad = "******";
// testcases for 0, 4, 8 characters
String input = "" | "abcd" | "abcdefgh"
左填充,不限制
result = pad.substring(Math.min(input.length(),pad.length())) + input;
results: "******" | "**abcd" | "abcdefgh"
右侧填充,不限制长度
result = input + pad.substring(Math.min(input.length(),pad.length()));
results: "******" | "abcd**" | "abcdefgh"
向左填充,限制填充长度
result = (pad + input).substring(input.length(), input.length() + pad.length());
results: "******" | "**abcd" | "cdefgh"
向右填充,限制填充长度
result = (input + pad).substring(0, pad.length());
results: "******" | "abcd**" | "abcdef"
java.util.Formatter
可以进行左右对齐。没有必要添加奇怪的第三方依赖(您会为如此微不足道的事情添加它们吗)。
(我省略了细节并将此帖子设置为“社区wiki”,因为我没有这方面的需求。)
AbstractStringBuilder append(CharSequence s, int start, int end) ;
private static final String MAX_STRING = " "; //20 spaces
Set<StringBuilder> set= new HashSet<StringBuilder>();
set.add(new StringBuilder("12345678"));
set.add(new StringBuilder("123456789"));
set.add(new StringBuilder("1234567811"));
set.add(new StringBuilder("12345678123"));
set.add(new StringBuilder("1234567812234"));
set.add(new StringBuilder("1234567812222"));
set.add(new StringBuilder("12345678122334"));
for(StringBuilder padMe: set)
padMe.append(MAX_STRING, padMe.length(), MAX_STRING.length());
public static String padRight(String s, int n, char padding){
StringBuilder builder = new StringBuilder(s.length() + n);
builder.append(s);
for(int i = 0; i < n; i++){
builder.append(padding);
}
return builder.toString();
}
public static String padLeft(String s, int n, char padding) {
StringBuilder builder = new StringBuilder(s.length() + n);
for(int i = 0; i < n; i++){
builder.append(Character.toString(padding));
}
return builder.append(s).toString();
}
public static String pad(String s, int n, char padding){
StringBuilder pad = new StringBuilder(s.length() + n * 2);
StringBuilder value = new StringBuilder(n);
for(int i = 0; i < n; i++){
pad.append(padding);
}
return value.append(pad).append(s).append(pad).toString();
}
padLeft(text, desiredLength - text.length(), ' ')
来完成这个任务。 - Aelphaeis这是一个高效的实用类,用于在Java中进行字符串的左侧填充、右侧填充、居中填充和零填充。
package com.example;
/**
* Utility class for left pad, right pad, center pad and zero fill.
*/
public final class StringPadding {
public static String left(String string, int length, char fill) {
if (string.length() < length) {
char[] chars = string.toCharArray();
char[] output = new char[length];
int delta = length - chars.length;
for (int i = 0; i < length; i++) {
if (i < delta) {
output[i] = fill;
} else {
output[i] = chars[i - delta];
}
}
return new String(output);
}
return string;
}
public static String right(String string, int length, char fill) {
if (string.length() < length) {
char[] chars = string.toCharArray();
char[] output = new char[length];
for (int i = 0; i < length; i++) {
if (i < chars.length) {
output[i] = chars[i];
} else {
output[i] = fill;
}
}
return new String(output);
}
return string;
}
public static String center(String string, int length, char fill) {
if (string.length() < length) {
char[] chars = string.toCharArray();
int delta = length - chars.length;
int a = (delta % 2 == 0) ? delta / 2 : delta / 2 + 1;
int b = a + chars.length;
char[] output = new char[length];
for (int i = 0; i < length; i++) {
if (i < a) {
output[i] = fill;
} else if (i < b) {
output[i] = chars[i - a];
} else {
output[i] = fill;
}
}
return new String(output);
}
return string;
}
public static String zerofill(String string, int length) {
return left(string, length, '0');
}
private StringPadding() {
}
/**
* For tests!
*/
public static void main(String[] args) {
String string = "123";
char blank = ' ';
System.out.println("left pad: [" + StringPadding.left(string, 10, blank) + "]");
System.out.println("right pad: [" + StringPadding.right(string, 10, blank) + "]");
System.out.println("center pad: [" + StringPadding.center(string, 10, blank) + "]");
System.out.println("zero fill: [" + StringPadding.zerofill(string, 10) + "]");
}
}
left pad: [ 123]
right pad: [123 ]
center pad: [ 123 ]
zero fill: [0000000123]
另一个使用递归的解决方案。
这个解决方案与所有JDK版本兼容,不需要外部库:
private static String addPadding(final String str, final int desiredLength, final String padBy) {
String result = str;
if (str.length() >= desiredLength) {
return result;
} else {
result += padBy;
return addPadding(result, desiredLength, padBy);
}
}
注意: 此解决方案将添加填充,稍微调整即可在填充值前缀中使用。
private static String padRight(String str, String padChar, int n) {
String paddedString = str;
while (paddedString.length() < n) {
paddedString = padChar + str;
}
return paddedString;
}
private static String padLeft(String str, String padChar, int n) {
String paddedString = str;
while (paddedString.length() < n) {
paddedString += padChar;
}
return paddedString;
}
就我个人而言,我正在寻找一些能够填充空白的东西,然后我决定自己编写代码。它相当简洁,您可以轻松地从中推导出padLeft和padRight。
/**
* Pads around a string, both left and right using pad as the template, aligning to the right or left as indicated.
* @param a the string to pad on both left and right
* @param pad the template to pad with, it can be of any size
* @param width the fixed width to output
* @param alignRight if true, when the input string is of odd length, adds an extra pad char to the left, so values are right aligned
* otherwise add an extra pad char to the right. When the input is of even length no extra chars will be inserted
* @return the input param a padded around.
*/
public static String padAround(String a, String pad, int width, boolean alignRight) {
if (pad.length() == 0)
throw new IllegalArgumentException("Pad cannot be an empty string!");
int delta = width - a.length();
if (delta < 1)
return a;
int half = delta / 2;
int remainder = delta % 2;
String padding = pad.repeat(((half+remainder)/pad.length()+1)); // repeating the padding to occupy all possible space
StringBuilder sb = new StringBuilder(width);
// sb.append( padding.substring(0,half + (alignRight ? 0 : remainder)));
sb.append(padding, 0, half + (alignRight ? 0 : remainder));
sb.append(a);
// sb.append( padding.substring(0,half + (alignRight ? remainder : 0)));
sb.append(padding, 0, half + (alignRight ? remainder : 0));
return sb.toString();
}
虽然它应该相当快,但可能会从这里和那里使用一些final受益。
稍微概括一下Eko的答案(Java 11+):
public class StringUtils {
public static String padLeft(String s, char fill, int padSize) {
if (padSize < 0) {
var err = "padSize must be >= 0 (was " + padSize + ")";
throw new java.lang.IllegalArgumentException(err);
}
int repeats = Math.max(0, padSize - s.length());
return Character.toString(fill).repeat(repeats) + s;
}
public static String padRight(String s, char fill, int padSize) {
if (padSize < 0) {
var err = "padSize must be >= 0 (was " + padSize + ")";
throw new java.lang.IllegalArgumentException(err);
}
int repeats = Math.max(0, padSize - s.length());
return s + Character.toString(fill).repeat(repeats);
}
public static void main(String[] args) {
System.out.println(padLeft("", 'x', 5)); // => xxxxx
System.out.println(padLeft("1", 'x', 5)); // => xxxx1
System.out.println(padLeft("12", 'x', 5)); // => xxx12
System.out.println(padLeft("123", 'x', 5)); // => xx123
System.out.println(padLeft("1234", 'x', 5)); // => x1234
System.out.println(padLeft("12345", 'x', 5)); // => 12345
System.out.println(padLeft("123456", 'x', 5)); // => 123456
System.out.println(padRight("", 'x', 5)); // => xxxxx
System.out.println(padRight("1", 'x', 5)); // => 1xxxx
System.out.println(padRight("12", 'x', 5)); // => 12xxx
System.out.println(padRight("123", 'x', 5)); // => 123xx
System.out.println(padRight("1234", 'x', 5)); // => 1234x
System.out.println(padRight("12345", 'x', 5)); // => 12345
System.out.println(padRight("123456", 'x', 5)); // => 123456
System.out.println(padRight("1", 'x', -1)); // => throws
}
}
这里有一个并行版本,适用于那些具有非常长字符串的人们 :-)
int width = 100;
String s = "129018";
CharSequence padded = IntStream.range(0,width)
.parallel()
.map(i->i-(width-s.length()))
.map(i->i<0 ? '0' :s.charAt(i))
.collect(StringBuilder::new, (sb,c)-> sb.append((char)c), (sb1,sb2)->sb1.append(sb2));