Java替換字串前後的指定字元（類似於String的trim()方法）

想到了替換字串或者正則表示式，但是沒想到怎麼實現！

看來平常得多看看原始碼！！！

2種實現方法，第一種簡單但不效率低，不推薦；第二種參考JDK的方法實現，高效，推薦。實現方法如下：

方法1：

用JDK自帶的trim方法加replace方法：

String str = "+++hello world+-,nihao!++++";
//傳字元
System.out.println(str.replace('+',' ').trim().replace(' ', '+'));
//或傳字串
//System.out.println(str.replace("+"," ").trim().replace(" ", "+"));
 

方法2：

JDK自帶的trim方法：

public String trim() {
        int len = value.length;
        int st = 0;
        char[] val = value;

        while ((st < len) && (val[st] <= ' ')) {
            st++;
        }
        while ((st < len) && (val[len - 1] <= ' ')) {
            len--;
        }
        return
 
 ((st > 0) || (len < value.length)) ? substring(st, len) : this;
    }

參考上面JDK自帶的trim方法,實現如下：

public static String custom_trim(String str, char c) {
        char[] chars = str.toCharArray();
        int len = chars.length;
        int st = 0;
        while ( (st < len) && (chars[st] == c) ){
            st ++;
        }
        while
 
 ( (st < len) && (chars[len-1] == c) ){
            len --;
        }

        return (st >0) && (len<chars.length)? str.substring(st, len): str;

    }

擴充套件：

JDK（1.7）的String類中沒有ltrim()和rtrim()方法，現在實現如下：

    public static String custom_ltrim(String str, char c) {
        char[] chars = str.toCharArray();
        int len = chars.length;
        int st = 0;
        while ( (st < len) && (chars[st] == c) ){
            st ++;
        }
        return (st >0)? str.substring(st, len): str;
    }

    public static String custom_rtrim(String str, char c) {
        char[] chars = str.toCharArray();
        int len = chars.length;
        int st = 0;
        while ( (st < len) && (chars[len-1] == c) ){
            len --;
        }
        return (len<chars.length)? str.substring(st, len): str;
    }

完整例項如下：

/**
 * 自定義字串修剪方法
 * Created by [email protected] on 18/3/10.
 */
public class TrimDemo {
    public static void main(String[] args) {
        String str = "+++hello world+-,nihao!++++";
        System.out.println(str.replace('+',' ').trim().replace(' ', '+'));//hello+world+-,nihao!
        System.out.println(str.replace("+"," ").trim().replace(" ", "+"));//hello+world+-,nihao!
        System.out.println(custom_trim(str, '+'));//hello world+-,nihao!
        System.out.println(custom_ltrim(str, '+'));//hello world+-,nihao!++++
        System.out.println(custom_rtrim(str, '+'));//+++hello world+-,nihao!
    }

    /**
     * 去掉指定字串前面和後面指定的字元
     * @param str
     * @param c
     * @return
     */
    public static String custom_trim(String str, char c) {
        char[] chars = str.toCharArray();
        int len = chars.length;
        int st = 0;
        while ( (st < len) && (chars[st] == c) ){
            st ++;
        }
        while ( (st < len) && (chars[len-1] == c) ){
            len --;
        }
        return (st >0) && (len<chars.length)? str.substring(st, len): str;
    }

    /**
     * 去掉指定字串前面指定的字元
     * @param str
     * @param c
     * @return
     */
    public static String custom_ltrim(String str, char c) {
        char[] chars = str.toCharArray();
        int len = chars.length;
        int st = 0;
        while ( (st < len) && (chars[st] == c) ){
            st ++;
        }
        return (st >0)? str.substring(st, len): str;
    }

    /**
     * 去掉指定字串後面指定的字元
     * @param str
     * @param c
     * @return
     */
    public static String custom_rtrim(String str, char c) {
        char[] chars = str.toCharArray();
        int len = chars.length;
        int st = 0;
        while ( (st < len) && (chars[len-1] == c) ){
            len --;
        }
        return (len<chars.length)? str.substring(st, len): str;
    }
}