去掉字符串中间的空格

/** * Created by king on 2017/5/8. * 功能：去掉中间的空格，保留两边的空格。 */public class Trimid {    public static void main(String[] args) {        String a1 = "   asd  fa  sdf   ";        String a2 = "   asd  fa  sdf";        String a3 = "asd  fa  sdf   ";        String a4 = "   asdfasdf   ";        String a5 = "asdfasdf";        String a6 = "       ";        System.out.println("--->" + trimid(a1) + "<---");        System.out.println("--->" + trimid(a2) + "<---");        System.out.println("--->" + trimid(a3) + "<---");        System.out.println("--->" + trimid(a4) + "<---");        System.out.println("--->" + trimid(a5) + "<---");        System.out.println("--->" + trimid(a6) + "<---");    }    private static String trimid(String a) {        int start = 0;        int end = a.length() - 1;        StringBuilder sb = new StringBuilder();        while (start < end && a.charAt(start) == ' ') start++;        while (start < end && a.charAt(end) == ' ') end--;        int i = start;        int j = start;        for (; i < end; i++) {            if (a.charAt(i) != ' ' && a.charAt(i + 1) == ' ') {                sb.append(a.substring(start, i + 1));            }            if (a.charAt(i) == ' ' && a.charAt(i + 1) != ' ') {                start = i + 1;            }        }        sb.append(a.substring(start, a.length())).insert(0, a.substring(0, j));        return sb.toString();    }}