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

public String replace(char oldChar, char newChar) {
    if (oldChar != newChar) {
        int len = value.length;
        int i = -1;
        char[] val = value; 

        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;
}

public String replaceFirst(String regex, String replacement) {
    return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
}


public String replaceAll(String regex, String replacement) {
    return Pattern.compile(regex).matcher(this).replaceAll(replacement);
}


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