replace(String, String) for java 1.3

/**
* 竟然淪落到自己補充api....Q口Q
* java 1.3這種老東西...該換了吧
* 更蠢的是...等我寫完才說有open source能用...
* 下次早點說呀！(昇龍拳)
*/

public static String replace(String target, String oldStr, String newStr){
StringBuffer tar = new StringBuffer();
int idx = 0;
for(;idx if(target.indexOf(oldStr,idx)==-1){
tar.append(target.substring(idx));
idx+=target.substring(idx).length();
}else{
tar.append(target.substring(idx,target.indexOf(oldStr,idx)));
tar.append(newStr);
idx=target.indexOf(oldStr,idx)+(oldStr.length());
}
}
return tar.toString();
}