字符串：替换空格

public class Solution {
    public String replaceSpace(StringBuffer str) {
        return str.toString().replaceAll("\\s+", "%20");
    }
}

public class Solution {
    public String replaceSpace(StringBuffer str) {
                String sti = str.toString();
        char[] strChar = sti.toCharArray();
        StringBuffer stb = new StringBuffer();
        for(int i=0;i<strChar.length;i++){
            if(strChar[i]==‘ ‘){
                stb.append("%20");
            }else{
                stb.append(strChar[i]);
            }
        }
        return stb.toString();
    }
}