Java 字符串对齐（使用String.format方法 ）

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编写StringAlign类实现字符串吧对齐。

import java.util.*;
import java.text.*;
import static java.lang.System.*;

public class StringAlign extends Format {
	
	private static final long serialVersion = 1L;
	
	/*枚举，哪种对齐方式*/
	public enum Alignment{
		/*左对齐*/
		LEFT,
		/*居中对齐*/
		CENTER,
		/*右对齐*/
		RIGHT,
	}
	
	private Alignment aligment;//当前对齐
	private int maxPages;//当前最大长度
	
	/*构造方法，用来设置字符串的居中方式以及最大长度*/
	public StringAlign(int maxPages, Alignment alignment) {
		
		switch(alignment) {
		case LEFT:
		case CENTER:
		case RIGHT:
			this.aligment = alignment;//将传过来的对齐方式赋值给全局的alignment变量
			break;
			
		default:
			throw new IllegalArgumentException("对齐参数错误！");
		}
		
		if(maxPages < 0) {//长度为负数时会抛出异常
			throw new IllegalArgumentException("页数参数错误");
		}
		
		this.maxPages = maxPages;
		
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		out.println("房东电话给一还是对方国家偶数个佛山东方宫is东方精工静极思动if个");//随便打的字，只是用来测试
		out.println();
		
		StringAlign align = new StringAlign(50, StringAlign.Alignment.CENTER);//调用构造方法，设置字符串对齐为居中对齐，最大长度为50
		
		out.println(align.format("- i -"));
		
		out.println(align.format(Integer.toString(10)));

	}

	@Override
	public StringBuffer format(Object input, StringBuffer where, FieldPosition ignore) {
		// TODO Auto-generated method stub
		String s = input.toString();
		String wanted = s.substring(0,Math.min(s.length(), maxPages));
		
		//得到右侧的空格
		switch(aligment) {
		case RIGHT:
			pad(where, maxPages - wanted.length());
			where.append(wanted);
			break;
		case CENTER:
			int toAdd = maxPages - wanted.length();
			pad(where, toAdd/2);
			where.append(wanted);
			pad(where, toAdd-toAdd/2);
			break;
		case LEFT:
			where.append(wanted);
			pad(where, maxPages-wanted.length());
			break;
		}
		return where;
	}

	private void pad(StringBuffer where, int howMany) {
		// TODO Auto-generated method stub
		for(int i = 0; i < howMany; i++) {
			where.append(' ');//添加空格
		}
	}
	
	String format(String s) {
		return format(s, new StringBuffer(), null).toString();
	}

	@Override
	public Object parseObject(String source, ParsePosition pos) {//用处不大
		// TODO Auto-generated method stub
		return source;
	}

}