为什么会提示返回值错误？

[hshl]

代码如下：
package db;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.ObjectInputStream;
import org.apache.jasper.runtime.*;
import org.apache.jasper.JasperException;
import java.beans.*;
public class t{
PageContext pageContext=null;
private String a1="From bean output!";
JspWriter out=pageContext.getOut();
public String geta(){
try{
out.write(a1);
}
catch(Exception e){
e.printStackTrace();
}
}
}