import java.text.*;

public class StringAlign extends Format{

public static final int JUST_LEFT='l'; //左对齐常量

public static final int JUST_RIGHT='r'; //右对齐常量

public static final int JUST_CENTER='c'; //居中常量

private int just; //当前的对其

private int maxChars;

public StringAlign(int maxChars,int just){

switch (just) {

case JUST_CENTER:

case JUST_LEFT:

case JUST_RIGHT:

this.just=just;

break;

default:

throw new IllegalArgumentException("invalid justification arg.");

}

if(maxChars<0){

throw new IllegalArgumentException("必须是正数！");

}

this.maxChars=maxChars;

}

public StringBuffer format(Object obj,StringBuffer where,FieldPosition ignore){

String s=(String)obj;

String wanted=s.substring(0, Math.min(s.length(), maxChars));

//如果没有空间用于对齐，则返回最大行宽的内容

if(wanted.length()>maxChars){

where.append(wanted);

}

else switch (just) {

case JUST_RIGHT:

pad(where,maxChars-wanted.length());

where.append(wanted);

break;

case JUST_LEFT:

where.append(wanted);

pad(where,maxChars-wanted.length());

break;

case JUST_CENTER:

int startPos=where.length();

pad(where,(maxChars-wanted.length())/2);

where.append(wanted);

pad(where,(maxChars-wanted.length())/2);

//调整化整误差

pad(where,maxChars-(where.length()-startPos));

break;

}

return where;

}

protected final void pad(StringBuffer to,int howMany){

for(int i=0;i<howMany;i++){

to.append(' ');

}

}

String format(String s){

return format(s,new StringBuffer(),null).toString();

}

@Override

public Object parseObject(String source, ParsePosition pos) {

// TODO Auto-generated method stub

return source;

}

}