使用StringBuilder将字符串用空格或其他字符填充 [英] Use StringBuilder to pad String with blank spaces or other characters
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问题描述
我是Java的初学者，这是我有关Stackoverflow的第一篇文章.尽管我的初始代码与此处的其他帖子相似，但我的问题与实现StringBuilder有关，因此我也提出了此帖子的原因.
I'm a beginner to java and this is my first post on Stackoverflow. Although my initial code is similar to other posts here, my question relates to implementing StringBuilder and so the reason for this post.
我已经创建了一个方法
**Initial code**
private static String padAgain(String result,int padNum)
{
String str = "";
for(int i = padNum; i >= 0; i--)
{
str = String.format("%" + padNum + "s", result).replace(" ", "*");
}
return str;
}
使用String.format方法在字符串的左边用空格(或特殊字符)填充.我在程序中使用相同的代码来证明数字的正确性.数字以2(个位数)开头，并以2的倍数增加(包含n个数字)，空格与数字的增加成反比.
to left pad the string with blank spaces (or special characters) using String.format method. I'm using the same in my program to right justify numbers. Numbers start with 2 (single-digit) and increase in multiples of 2 (containing n no. of digits) with the spaces being inversely proportional to the increase in digits.
以下是出于说明目的的输出:
Here is the output for illustrative purposes:
Enter exponent value for base-2 - Enter 0 to exit:
128
Square 1: **************************************2 items
Square 2: **************************************4 items
Square 3: **************************************8 items
Square 4: *************************************16 items
Square 5: *************************************32 items
Square 6: *************************************64 items
Square 7: ************************************128 items
Square 8: ************************************256 items
Square 9: ************************************512 items
Square 10: ***********************************1024 items
Square 11: ***********************************2048 items
Square 12: ***********************************4096 items
Square 13: ***********************************8192 items
Square 14: **********************************16384 items
Square 15: **********************************32768 items
Square 16: **********************************65536 items
Square 17: *********************************131072 items
Square 18: *********************************262144 items
Square 19: *********************************524288 items
Square 20: ********************************1048576 items
Square 21: ********************************2097152 items
Square 22: ********************************4194304 items
Square 23: ********************************8388608 items
Square 24: *******************************16777216 items
Square 25: *******************************33554432 items
Square 26: *******************************67108864 items
Square 27: ******************************134217728 items
Square 28: ******************************268435456 items
Square 29: ******************************536870912 items
Square 30: *****************************1073741824 items
Square 31: *****************************2147483648 items
Square 32: *****************************4294967296 items
Square 33: *****************************8589934592 items
Square 34: ****************************17179869184 items
Square 35: ****************************34359738368 items
Square 36: ****************************68719476736 items
Square 37: ***************************137438953472 items
Square 38: ***************************274877906944 items
Square 39: ***************************549755813888 items
Square 40: **************************1099511627776 items
Square 41: **************************2199023255552 items
Square 42: **************************4398046511104 items
Square 43: **************************8796093022208 items
Square 44: *************************17592186044416 items
Square 45: *************************35184372088832 items
Square 46: *************************70368744177664 items
Square 47: ************************140737488355328 items
Square 48: ************************281474976710656 items
Square 49: ************************562949953421312 items
Square 50: ***********************1125899906842624 items
Square 51: ***********************2251799813685248 items
Square 52: ***********************4503599627370496 items
Square 53: ***********************9007199254740992 items
Square 54: **********************18014398509481984 items
Square 55: **********************36028797018963968 items
Square 56: **********************72057594037927936 items
Square 57: *********************144115188075855872 items
Square 58: *********************288230376151711744 items
Square 59: *********************576460752303423488 items
Square 60: ********************1152921504606846976 items
Square 61: ********************2305843009213693952 items
Square 62: ********************4611686018427387904 items
Square 63: ********************9223372036854775808 items
Square 64: *******************18446744073709551616 items
Square 65: *******************36893488147419103232 items
Square 66: *******************73786976294838206464 items
Square 67: ******************147573952589676412928 items
Square 68: ******************295147905179352825856 items
Square 69: ******************590295810358705651712 items
Square 70: *****************1180591620717411303424 items
Square 71: *****************2361183241434822606848 items
Square 72: *****************4722366482869645213696 items
Square 73: *****************9444732965739290427392 items
Square 74: ****************18889465931478580854784 items
Square 75: ****************37778931862957161709568 items
Square 76: ****************75557863725914323419136 items
Square 77: ***************151115727451828646838272 items
Square 78: ***************302231454903657293676544 items
Square 79: ***************604462909807314587353088 items
Square 80: **************1208925819614629174706176 items
Square 81: **************2417851639229258349412352 items
Square 82: **************4835703278458516698824704 items
Square 83: **************9671406556917033397649408 items
Square 84: *************19342813113834066795298816 items
Square 85: *************38685626227668133590597632 items
Square 86: *************77371252455336267181195264 items
Square 87: ************154742504910672534362390528 items
Square 88: ************309485009821345068724781056 items
Square 89: ************618970019642690137449562112 items
Square 90: ***********1237940039285380274899124224 items
Square 91: ***********2475880078570760549798248448 items
Square 92: ***********4951760157141521099596496896 items
Square 93: ***********9903520314283042199192993792 items
Square 94: **********19807040628566084398385987584 items
Square 95: **********39614081257132168796771975168 items
Square 96: **********79228162514264337593543950336 items
Square 97: *********158456325028528675187087900672 items
Square 98: *********316912650057057350374175801344 items
Square 99: *********633825300114114700748351602688 items
Square 100: ********1267650600228229401496703205376 items
Square 101: ********2535301200456458802993406410752 items
Square 102: ********5070602400912917605986812821504 items
Square 103: *******10141204801825835211973625643008 items
Square 104: *******20282409603651670423947251286016 items
Square 105: *******40564819207303340847894502572032 items
Square 106: *******81129638414606681695789005144064 items
Square 107: ******162259276829213363391578010288128 items
Square 108: ******324518553658426726783156020576256 items
Square 109: ******649037107316853453566312041152512 items
Square 110: *****1298074214633706907132624082305024 items
Square 111: *****2596148429267413814265248164610048 items
Square 112: *****5192296858534827628530496329220096 items
Square 113: ****10384593717069655257060992658440192 items
Square 114: ****20769187434139310514121985316880384 items
Square 115: ****41538374868278621028243970633760768 items
Square 116: ****83076749736557242056487941267521536 items
Square 117: ***166153499473114484112975882535043072 items
Square 118: ***332306998946228968225951765070086144 items
Square 119: ***664613997892457936451903530140172288 items
Square 120: **1329227995784915872903807060280344576 items
Square 121: **2658455991569831745807614120560689152 items
Square 122: **5316911983139663491615228241121378304 items
Square 123: *10633823966279326983230456482242756608 items
Square 124: *21267647932558653966460912964485513216 items
Square 125: *42535295865117307932921825928971026432 items
Square 126: *85070591730234615865843651857942052864 items
Square 127: 170141183460469231731687303715884105728 items
Square 128: 340282366920938463463374607431768211456 items
Enter exponent value for base-2 - Enter 0 to exit:
0
当迭代次数从2 ^ 10到2 ^ 128呈指数增长时，String.format()似乎有点慢. 因此，我用StringBuilder替换了String.format，但只获得了部分成功.
When the iterations increase exponentially, say from 2^10 to 2^128, then the String.format() seems to be a tad slow. So, I replaced String.format with StringBuilder and met only with partial success.
[sidebar]为简洁起见，我没有发布程序代码的其余部分，我的重点是所示的padAgain(String，int)方法.如果需要，将发布整个代码.[/sidebar]
[sidebar]I've not posted rest of the program code for brevity and also my focus is on padAgain(String,int) method shown.If required, will post entire code.[/sidebar]
**Initial code modified**
private static String padAgain(String result,int padNum)
{
StringBuilder sb = new StringBuilder(result);
for(int i = 1; i < padNum; i++)
{
sb.insert(0, result).insert(sb.indexOf(result), " ").setLength(padNum - result.toCharArray().length);
}
sb.append(result);
return sb.toString();
}
及其输出
Enter exponent value for base-2 - Enter 0 to exit:
16
Square 1: 2 22 items
Square 2: 4 44 items
Square 3: 8 88 items
Square 4: 1616 items
Square 5: 3232 items
Square 6: 6464 items
Square 7: 1128 items
Square 8: 2256 items
Square 9: 5512 items
Square 10: 1024 items
Square 11: 2048 items
Square 12: 4096 items
Square 13: 8192 items
Square 14: 16384 items
Square 15: 32768 items
Square 16: 65536 items
Enter exponent value for base-2 - Enter 0 to exit:
0
代码说明(我正在尝试做的事情):
- 变量"padNum"存储指数值的最大长度， 最高为65536.长度5
- 变量结果"是以数字开头的字符串表示形式 2
- for循环迭代到最大.达到长度
- StringBuilder对象，用于在索引0处插入String值. 为此，通过将结果"作为子字符串传递来调用indexOf(String) 并在位置0处插入空格，最大长度为- 每个数字的长度
- 最后附加结果"以构成最大值.长度和
- 作为字符串值返回到调用对象
- variable 'padNum' stores the maximum length of the exponent value, being 65536 of max. length 5
- variable 'result' is a String representation of numbers starting with 2
- for loop to iterate till max. length is reached
- StringBuilder object to insert the String value at index 0. Within this, invoke the indexOf(String) by passing 'result' as a substring of itself and insert blank space at position 0 upto max.length - length of each number
- finally append 'result' to make up the max. length and
- return as String value to calling object
非常感谢论坛专家/成员可以帮助扩展/进一步修改/纠正我的StringBuilder代码.
Much appreciated if the forum experts/members could help expand/further modify/correct my StringBuilder code.
推荐答案
您还可以使用Arrays的fill()方法更简单一些.
You can also something really simpler with the fill() method of Arrays.
StringBuilder sb = new StringBuilder();
char[] pad = new char[padnum - result.length()];
Arrays.fill(pad, '*');
return sb.append(pad).append(result).toString();
我们的时间很少，但是这种方法比 for循环方法快25％.
We are in really little times but this method is about 25% faster than the for loop one.
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