浣滆?eckel_cn
鏈榪?闂叉殗涔嬩綑,閲嶆柊鏁寸悊鑷敤鐨凷tringUtil綾?鍦ㄦ暣鐞嗗埌repeat鏂規硶(閲嶅瀛楃涓?鏃?鍙戠幇鍏跺瓨鍦ㄦ晥鐜囬棶棰?渚挎墦綆楅噸鏂板啓涓涓?鍗村彂鐜頒簡涓緋誨垪浠ュ墠娌″お娉ㄦ剰鐨勪笢瑗?瑙夊緱寰堟湁蹇呰鍐欎笅鏉?
鍘熸潵榪欎釜repeat鏂規硶,寰堢畝鍗?涓昏浠ｇ爜澶ц嚧濡備笅:
1
public static String repeat1(String str, int n) 
{
2
StringBuffer strBuf = new StrBuffer(str.length()*n);
3
for(int i - 0; i < n; i++) {
4 strBuf.append(str);
5
}
6retrn strBuf.toString();
7
}
public static String repeat1(String str, int n) {2
StringBuffer strBuf = new StrBuffer(str.length()*n);3
for(int i - 0; i < n; i++) {4
strBuf.append(str);5
}6
retrn strBuf.toString();7
} 鍒濅竴鐪?灝辮兘鍙戠幇涓鐐歸棶棰?褰搉寰堝ぇ,杈懼埌涓瀹氬ぇ灝?灝辮兘浣垮爢鏍堟孩鍑?鍑虹幇OutOfMemery閿欒.
閭ｅ浣曢伩鍏嶈繖涓棶棰樺憿,鎴戦┈涓婃兂鍒頒簡,鏃㈢劧StringBuffer鍜孲tring涓鏍峰唴閮ㄩ兘鏄湪鎿嶄綔char鏁扮粍,
閭ｆ垜灝辮嚜宸辯洿鎺ユ搷浣渃har鏁扮粍,鍦ㄦ渶灝戠殑寰幆閲岄潰,濉厖char鏁扮粍,浠ｇ爜濡備笅:
閭ｆ垜灝辮嚜宸辯洿鎺ユ搷浣渃har鏁扮粍,鍦ㄦ渶灝戠殑寰幆閲岄潰,濉厖char鏁扮粍,浠ｇ爜濡備笅:
1public static String repeat2(String str, int n) {
2 int len = str.length();
3 int maxlen = len * n;
4 char[] chars = new char[len * n];
5 str.getChars(0, len, chars, 0);
6 int count = len;
7 int copyLen = 0;
8 while ((copyLen = maxlen - count > count ? count : maxlen - count) > 0) {
9 System.arraycopy(chars, 0, chars, count, copyLen);
10 count += copyLen;
11 }
12 String outstr = new String(chars);
13 return outstr;
14}
public static String repeat2(String str, int n) {2
int len = str.length();3
int maxlen = len * n;4
char[] chars = new char[len * n];5
str.getChars(0, len, chars, 0);6
int count = len;7
int copyLen = 0;8
while ((copyLen = maxlen - count > count ? count : maxlen - count) > 0) {9
System.arraycopy(chars, 0, chars, count, copyLen);10
count += copyLen;11
}12
String outstr = new String(chars);13
return outstr;14
} 嫻嬭瘯鍚?鍙戠幇,寰幆鎺у埗鍦ㄤ簡鏈灝?浣嗘槸,鎬ц兘鍗磋繕涓嶅repeat1,涔熻浣犱細鍜屾垜涓鏍峰紑濮嬪緢鎯婅,浣嗙湅浜?BR>StringBuffer鐨勫疄鐜板悗,鍙戠幇repeat2鐨勫疄鐜頒腑,灝哻har鏁扮粍,杞崲涓篠tring,鏄晥鐜囧涔堜綆鐨勪簨鎯?榪欎釜榪囩▼闇瑕佸湪String鍐呴儴閲嶆柊鍒涘緩涓涓猚har鏁扮粍,鐒跺悗鎶婁紶榪涘幓鐨刢har鏁扮粍,澶嶅埗緇欏畠.鑰宺epeat1涓負浠涔堟病鏈夎繖涓ц兘闂鍛?鍏跺疄榪欏氨鏄褰掑姛浜嶴UN鍦ㄥ疄鐜癝tringBuffer涓殑涓涓噸瑕佸睘鎬?shared,褰撲綘浣跨敤StringBuffer鍚?鎯沖緱鍒癝tring鏃?String浼氬叡浜玈tringBuffer涓殑char鏁扮粍,榪欐牱涓鏉?鎬ц兘闈炲父楂?
鍏變韓浼氫笉浼氬甫鏉ュ壇浣滅敤鍛?SUN鐨勫疄鐜板綋鐒惰冭檻鍒頒簡,鍦ㄦ敼鍙楽tringBuffer鏃?濡傛灉榪欎釜StringBuffer
鏈夊叾浠朣tring鍏變韓瀹冪殑char鏁扮粍鏃?StringBuffer灝辨妸榪欎釜char鏁扮粍璁╃粰String,鑷繁閲嶆柊澶嶅埗涓浠戒嬌鐢?
鍏變韓浼氫笉浼氬甫鏉ュ壇浣滅敤鍛?SUN鐨勫疄鐜板綋鐒惰冭檻鍒頒簡,鍦ㄦ敼鍙楽tringBuffer鏃?濡傛灉榪欎釜StringBuffer
鏈夊叾浠朣tring鍏變韓瀹冪殑char鏁扮粍鏃?StringBuffer灝辨妸榪欎釜char鏁扮粍璁╃粰String,鑷繁閲嶆柊澶嶅埗涓浠戒嬌鐢?
鏃㈢劧闂鍙戠幇浜?鎴戝張鎹簡縐嶇畻娉曟潵瀹炵幇,鍚屾牱涔熸槸鎶婂驚鐜帶鍒跺湪鏈灝?鍚屾椂瑙ｅ喅杞崲甯︽潵鐨勬晥鐜囦綆涓嬮棶棰?
綆楁硶瀹炵幇,鍐嶆嫻嬭瘯,嫻嬭瘯鍙戠幇,鍦ㄨ妯′笉鏄壒鍒ぇ鐨勬儏鍐典笅,repeat3鐨勬晥鐜囪鏄庢樉浼樹簬鍓嶄袱涓?浣嗗湪瑙勬ā澶х殑鎯呭喌涓?浼氬彉鐨勫樊涓嶅,鎬庝箞浼氳繖鏍風殑鍛?鍐嶆榪涜娣卞叆璋冩煡,緇撴灉鍙戠幇鏄疭UN鐨凷ystem.arrayCopy榪欎釜鏂規硶鏈夋ц兘闂,鐗瑰埆鏄綋瑕佸鍒剁殑闀垮害鐗瑰埆澶х殑鎯呭喌涓?鎬ц兘涓嬮檷鐨勬瘮杈冨揩,鍐嶆崲涓狪BM鐨凧DK瀹炵幇,鍙堝彂鐜?IBM鐨勮繖涓柟娉曠殑瀹炵幇瑕佹瘮SUN鏈夋敼榪?
1public static String repeat3(String str, int n) {
2 // if input string is null,return null.
3 if (null == str) {
4 return null;
5 }
6 final int strlen = str.length();
7 // if repeat number is less than two or given string's length is zero,
8 // then return the givien string.
9 if (2 > n || 0 == strlen) {
10 return str;
11 }
12 // assigns the enough size for the string buffer.
13 StringBuffer strBuf = new StringBuffer(strlen * n);
14 // get odd length flag.
15 final boolean oddLen = n % 2 == 1 ? true : false;
16 // calculates the grow times.
17 final int growTimes = (int) Math.floor(Math.log(n) / Math.log(2));
18 // adds one given string.
19 strBuf.append(str);
20 // grows until more than half of the repeat count.
21 for (int i = 0; i < growTimes; i++) {
22 strBuf.append(strBuf);
23 if (Math.pow(2, i - 1) * 2 < n && Math.pow(2, i) * 2 >= n) {
24 break;
25 }
26 }
27 // reset the string buffer's length to half of the repeat count.
28 strBuf.setLength(strlen * Math.round(n / 2));
29 // grows to the repeat count.
30 strBuf.append(strBuf);
31 if (oddLen) {
32 strBuf.append(str);
33 }
34 String returnStr = new String(strBuf);
35 return returnStr;
36}
37
public static String repeat3(String str, int n) {2
// if input string is null,return null.3
if (null == str) {4
return null;5
}6
final int strlen = str.length();7
// if repeat number is less than two or given string's length is zero,8
// then return the givien string.9
if (2 > n || 0 == strlen) {10
return str;11
}12
// assigns the enough size for the string buffer.13
StringBuffer strBuf = new StringBuffer(strlen * n);14
// get odd length flag.15
final boolean oddLen = n % 2 == 1 ? true : false;16
// calculates the grow times.17
final int growTimes = (int) Math.floor(Math.log(n) / Math.log(2));18
// adds one given string.19
strBuf.append(str);20
// grows until more than half of the repeat count.21
for (int i = 0; i < growTimes; i++) {22
strBuf.append(strBuf);23
if (Math.pow(2, i - 1) * 2 < n && Math.pow(2, i) * 2 >= n) {24
break;25
}26
}27
// reset the string buffer's length to half of the repeat count.28
strBuf.setLength(strlen * Math.round(n / 2));29
// grows to the repeat count.30
strBuf.append(strBuf);31
if (oddLen) {32
strBuf.append(str);33
}34
String returnStr = new String(strBuf);35
return returnStr;36
}37
綆楁硶瀹炵幇,鍐嶆嫻嬭瘯,嫻嬭瘯鍙戠幇,鍦ㄨ妯′笉鏄壒鍒ぇ鐨勬儏鍐典笅,repeat3鐨勬晥鐜囪鏄庢樉浼樹簬鍓嶄袱涓?浣嗗湪瑙勬ā澶х殑鎯呭喌涓?浼氬彉鐨勫樊涓嶅,鎬庝箞浼氳繖鏍風殑鍛?鍐嶆榪涜娣卞叆璋冩煡,緇撴灉鍙戠幇鏄疭UN鐨凷ystem.arrayCopy榪欎釜鏂規硶鏈夋ц兘闂,鐗瑰埆鏄綋瑕佸鍒剁殑闀垮害鐗瑰埆澶х殑鎯呭喌涓?鎬ц兘涓嬮檷鐨勬瘮杈冨揩,鍐嶆崲涓狪BM鐨凧DK瀹炵幇,鍙堝彂鐜?IBM鐨勮繖涓柟娉曠殑瀹炵幇瑕佹瘮SUN鏈夋敼榪?
鐪熸槸涓嬈℃瘮杈冩湁鎰忔濈殑娣卞叆StringBuffer,鍦ㄥ疄闄呰繍鐢ㄤ腑repeat3瀹屽叏鍙互浠ｆ浛涓婇潰涓ょ鏂規硶.
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