将数目字转为指定长度的字符串，如果位数不够，添加前缀 0

将数字转为指定长度的字符串，如果位数不够，添加前缀 0
呃。。。好象可以用 java.text.DecimalFormat。。。先研究一下这个类。

	/**
	 * 将数字转为指定长度的字符串，如果位数不够，添加前缀 0
	 * @param value
	 * @param length
	 * @return
	 */
	private static String i2s(int value, int length)
	{
//		System.out.println("value:" + value);
//		System.out.println("length:" + length);
		String s = String.valueOf(value);
		if(s.length()>length)
		{
			throw new RuntimeException("length is too short.");
		}
		else if(s.length()==length)
		{
			return s;
		}
		else
		{
			char[] cc = new char[length];
			int i=0;
			for(; i<length - s.length(); i++)
			{
				cc[i] = '0';
			}
			for(; i<length; i++)
			{
				//System.out.println(i);
				cc[i] = s.charAt(length - i - 1); //这里容易出错：length - i - 1
			}
			return new String(cc);
		}
	}

	private static void testI2s()
	{
		for (int i = 0; i < 1050; i++) {
			System.out.println(i2s(i, 3));
		}
	}

DecimalFormat 版

	private static String i2s_02(int value, int length)
	{
		//java.util.Formatter
		//DecimalFormat df = new DecimalFormat("###");
		//DecimalFormat df = new DecimalFormat("000");
		
		char[] cc = new char[length];
		int i=0;
		for(i=0; i<length; i++)
		{
			//cc[i] = '#';
			cc[i] = '0';
		}
		
		DecimalFormat df = new DecimalFormat( new String(cc) );
		
		String s = df.format(value);
		if(s.length()>length)
		{
			throw new RuntimeException("length is too short.");
		}
		return s;
	}
	
	
	private static void testI2s_02()
	{
		for (int i = 0; i < 1050; i++) {
			System.out.println(i2s_02(i, 3));
		}
	}