java-给定字符串，删除开始和结尾处的空格，并将中间的多个连续的空格合并成一个。...

public class DeleteExtraSpace {

	/**
	 * 题目：给定字符串，删除开始和结尾处的空格，并将中间的多个连续的空格合并成一个。
	 * 方法1.用已有的String类的trim和replaceAll方法
	 * 方法2.全部用正则表达式，这个我不熟
	 * 方法3.“重新发明轮子”，从头遍历一次
	 */
	public static void main(String[] args) {

		String[] strs={
				"",
				" ",
				"a",
				"  hello    world   ",
		};
		for(String str:strs){
			String str2=str.trim().replaceAll(" +", " ");
			System.out.println(str2+",length2="+str2.length());

			String str3=deleteExtraSpace(str);
			System.out.println(str3+",length3="+str3.length());

			System.out.println(str2.equals(str3));
			System.out.println("=========================");
		}

	}

	public static String deleteExtraSpace(String str){
		if(str==null){
			return null;
		}
		if(str.length()==0 || str.equals(" ")){
			return new String();
		}
		char[] oldStr=str.toCharArray();
		int len=str.length();
		char[] tmpStr=new char[len];
		boolean keepSpace=false;
		int j=0;//the index of new string
		for(int i=0;i			char tmpChar=oldStr[i];
			if(oldStr[i]!=' '){
				tmpStr[j++]=tmpChar;
				keepSpace=true;
			}else if(keepSpace){
				tmpStr[j++]=tmpChar;
				keepSpace=false;
			}
		}

		//unlike c/c++,no "\0" at the end of a string. So,do the copy again...
		int newLen=j;
		if(tmpStr[j-1]==' '){
			newLen--;
		}
		char[] newStr=new char[newLen];
		for(int i=0;i			newStr[i]=tmpStr[i];
		}
		return new String(newStr);
	}
}