有一些简单的方法来填充字符串在Java?
似乎是一些应该在一些stringutil类API,但我找不到任何东西,这样做。
有一些简单的方法来填充字符串在Java?
似乎是一些应该在一些stringutil类API,但我找不到任何东西,这样做。
当前回答
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
}
}
其他回答
Java联机程序,没有花哨的库。
// 6 characters padding example
String pad = "******";
// testcases for 0, 4, 8 characters
String input = "" | "abcd" | "abcdefgh"
左Pad,不要限制
result = pad.substring(Math.min(input.length(),pad.length())) + input;
results: "******" | "**abcd" | "abcdefgh"
右移,不要限制
result = input + pad.substring(Math.min(input.length(),pad.length()));
results: "******" | "abcd**" | "abcdefgh"
左衬垫,限制衬垫长度
result = (pad + input).substring(input.length(), input.length() + pad.length());
results: "******" | "**abcd" | "cdefgh"
右垫,限制垫的长度
result = (input + pad).substring(0, pad.length());
results: "******" | "abcd**" | "abcdef"
从Java 11开始,string. repeat(int)可以用来左右填充给定的字符串。
System.out.println("*".repeat(5)+"apple");
System.out.println("apple"+"*".repeat(5));
输出:
*****apple
apple*****
s =字符串填充 n =期望长度 c = Char到pad
private String padStart( String s, int n, char c ){
if( n <= 0 ) return s;
else return String.format("%" + n + "s", s).replace(' ', c);
}
这是一个高效的实用工具类,用于Java中的左填充,右填充,中心填充和零填充字符串。
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) + "]");
}
}
输出如下:
left pad: [ 123]
right pad: [123 ]
center pad: [ 123 ]
zero fill: [0000000123]
所有的字符串操作通常都需要非常高效——特别是当你处理大数据集的时候。我想要的东西是快速和灵活的,类似于你将在plsql pad命令。另外,我不想为一件小事包含一个巨大的库。考虑到这些因素,这些解决方案都不令人满意。这是我提出的解决方案,有最好的基准测试结果,如果有人可以改进它,请添加您的评论。
public static char[] lpad(char[] pStringChar, int pTotalLength, char pPad) {
if (pStringChar.length < pTotalLength) {
char[] retChar = new char[pTotalLength];
int padIdx = pTotalLength - pStringChar.length;
Arrays.fill(retChar, 0, padIdx, pPad);
System.arraycopy(pStringChar, 0, retChar, padIdx, pStringChar.length);
return retChar;
} else {
return pStringChar;
}
}
注意它是用String. tochararray()调用的,结果可以用new String((char[])result)转换为String。这样做的原因是,如果你应用多个操作,你可以在char[]上完成它们,而不需要在格式之间进行转换——在幕后,字符串存储为char[]。如果这些操作包含在String类本身中,那么效率将提高一倍——速度和内存方面。