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
你可以通过保留填充数据来减少每次调用的开销,而不是每次都重新构建:
public class RightPadder {
private int length;
private String padding;
public RightPadder(int length, String pad) {
this.length = length;
StringBuilder sb = new StringBuilder(pad);
while (sb.length() < length) {
sb.append(sb);
}
padding = sb.toString();
}
public String pad(String s) {
return (s.length() < length ? s + padding : s).substring(0, length);
}
}
作为一种替代方法,您可以将结果长度作为pad(…)方法的参数。在这种情况下,在该方法中而不是在构造函数中调整隐藏填充。
(提示:为了获得额外的学分,让它是线程安全的!: -)
其他回答
填充到10个字符:
String.format("%10s", "foo").replace(' ', '*');
String.format("%-10s", "bar").replace(' ', '*');
String.format("%10s", "longer than 10 chars").replace(' ', '*');
输出:
*******foo
bar*******
longer*than*10*chars
密码字符显示“*”:
String password = "secret123";
String padded = String.format("%"+password.length()+"s", "").replace(' ', '*');
输出与密码字符串长度相同:
secret123
*********
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]
另一种利用递归的解决方案。
这与所有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:这个解决方案将附加填充,与一个小调整,你可以前缀填充值。
使用该函数。
private String leftPadding(String word, int length, char ch) {
return (length > word.length()) ? leftPadding(ch + word, length, ch) : word;
}
如何使用?
leftPadding(month, 2, '0');
输出: 01 02 03 04 ..11日12
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
}
}