Java String replace replaceAll replaceFirst 执行效果笔记

代码

public static void main(String[] args) {String aa = "asdfghjklzxcvbnmasdfghjklzxcvbnmasdfghjklzxcvbnm";System.out.println(aa.replace('b', '1'));System.out.println(aa.replace("bnm", "123"));System.out.println(aa.replaceAll("bnm", "123"));System.out.println(aa.replaceFirst("bnm", "123"));
}

结果

asdfghjklzxcv1nmasdfghjklzxcv1nmasdfghjklzxcv1nm
asdfghjklzxcv123asdfghjklzxcv123asdfghjklzxcv123
asdfghjklzxcv123asdfghjklzxcv123asdfghjklzxcv123
asdfghjklzxcv123asdfghjklzxcvbnmasdfghjklzxcvbnm

replace 和 replaceAll 的效果都是全部替换
replaceFirst 的效果是替换首次出现的字符

/*** Returns a string resulting from replacing all occurrences of* {@code oldChar} in this string with {@code newChar}.* <p>* If the character {@code oldChar} does not occur in the* character sequence represented by this {@code String} object,* then a reference to this {@code String} object is returned.* Otherwise, a {@code String} object is returned that* represents a character sequence identical to the character sequence* represented by this {@code String} object, except that every* occurrence of {@code oldChar} is replaced by an occurrence* of {@code newChar}.* <p>* Examples:* <blockquote><pre>* "mesquite in your cellar".replace('e', 'o')*         returns "mosquito in your collar"* "the war of baronets".replace('r', 'y')*         returns "the way of bayonets"* "sparring with a purple porpoise".replace('p', 't')*         returns "starring with a turtle tortoise"* "JonL".replace('q', 'x') returns "JonL" (no change)* </pre></blockquote>** @param   oldChar   the old character.* @param   newChar   the new character.* @return  a string derived from this string by replacing every*          occurrence of {@code oldChar} with {@code newChar}.*/
public String replace(char oldChar, char newChar) {if (oldChar != newChar) {int len = value.length;int i = -1;char[] val = value; /* avoid getfield opcode */while (++i < len) {if (val[i] == oldChar) {break;}}if (i < len) {char buf[] = new char[len];for (int j = 0; j < i; j++) {buf[j] = val[j];}while (i < len) {char c = val[i];buf[i] = (c == oldChar) ? newChar : c;i++;}return new String(buf, true);}}return this;
}

/*** Replaces the first substring of this string that matches the given <a* href="../util/regex/Pattern.html#sum">regular expression</a> with the* given replacement.** <p> An invocation of this method of the form* <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}* yields exactly the same result as the expression** <blockquote>* <code>* {@link java.util.regex.Pattern}.{@link* java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link* java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link* java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)* </code>* </blockquote>**<p>* Note that backslashes ({@code \}) and dollar signs ({@code $}) in the* replacement string may cause the results to be different than if it were* being treated as a literal replacement string; see* {@link java.util.regex.Matcher#replaceFirst}.* Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special* meaning of these characters, if desired.** @param   regex*          the regular expression to which this string is to be matched* @param   replacement*          the string to be substituted for the first match** @return  The resulting {@code String}** @throws  PatternSyntaxException*          if the regular expression's syntax is invalid** @see java.util.regex.Pattern** @since 1.4* @spec JSR-51*/
public String replaceFirst(String regex, String replacement) {return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
}/*** Replaces each substring of this string that matches the given <a* href="../util/regex/Pattern.html#sum">regular expression</a> with the* given replacement.** <p> An invocation of this method of the form* <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}* yields exactly the same result as the expression** <blockquote>* <code>* {@link java.util.regex.Pattern}.{@link* java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link* java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link* java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)* </code>* </blockquote>**<p>* Note that backslashes ({@code \}) and dollar signs ({@code $}) in the* replacement string may cause the results to be different than if it were* being treated as a literal replacement string; see* {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.* Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special* meaning of these characters, if desired.** @param   regex*          the regular expression to which this string is to be matched* @param   replacement*          the string to be substituted for each match** @return  The resulting {@code String}** @throws  PatternSyntaxException*          if the regular expression's syntax is invalid** @see java.util.regex.Pattern** @since 1.4* @spec JSR-51*/
public String replaceAll(String regex, String replacement) {return Pattern.compile(regex).matcher(this).replaceAll(replacement);
}/*** Replaces each substring of this string that matches the literal target* sequence with the specified literal replacement sequence. The* replacement proceeds from the beginning of the string to the end, for* example, replacing "aa" with "b" in the string "aaa" will result in* "ba" rather than "ab".** @param  target The sequence of char values to be replaced* @param  replacement The replacement sequence of char values* @return  The resulting string* @since 1.5*/
public String replace(CharSequence target, CharSequence replacement) {return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(this).replaceAll(Matcher.quoteReplacement(replacement.toString()));
}

看源码 replace 的参数是 CharSequence 或者 char
        当参数是 char 时用 newChar 替换掉 oldChar
        当参数为 CharSequence 时最终调用的方法和 replaceAll 是同一个
replaceAll 的参数是 String ；支持字符串和正则表达式
        当参数传的是普通字符串时效果与 replace 一致
replaceFirst 的参数是 String ; 支持字符串和正则表达式
         替换首次匹配到的字符

参考博客

https://wenku.baidu.com/view/39b0d047deccda38376baf1ffc4ffe473368fdea.html
https://blog.csdn.net/atongmu2017/article/details/103889830
https://www.jb51.net/article/157844.htm

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