字符串全排列 java实现

package permStr;

public class PermStr
{
	public static final int SWITCH = 1; //是否去除重复的开关, 1表示去重, 0表示不去重, 默认为1
	private static boolean need_swap(StringBuilder str, int start, int i)
	{
		if(SWITCH == 0)
			return true;
		else
		{
			for(int j = start; j <= i - 1; j++)
			{
				if(str.charAt(j) == str.charAt(i))
					return false;
			}
			return true;
		}
	}
	public static void permStr(StringBuilder str, int start, int end)
	{
		if(start == end - 1)
		    System.out.println(str.toString());
		for(int i = start; i <= end - 1; i++)
		{
			if(need_swap(str, start, i)) 
			{
				swap(str, start, i);
				permStr(str, start + 1, end);
				swap(str, start, i);
			}
		}
	}
	
	private static void swap(StringBuilder str, int p, int q)
	{
		char temp = str.charAt(q);
		str.setCharAt(q, str.charAt(p));
		str.setCharAt(p, temp);
	}
	public static void main(String[] args)
	{
		StringBuilder str = new StringBuilder();
		str.append("abca");
		permStr(str, 0 , str.length());
	}
}