File和BufferedWriter每次都覆盖文件

public void addInfo()
{
try
{
File file = new File( "result.txt ");
if(!file.exists())
file.createNewFile();
String str = "学号: "+sNum.getText() + "," + "姓名: "+sName.getText() + "";

        BufferedWriter bw = new BufferedWriter(new FileWriter(file));

        bw.write(str);
        bw.write(13);
        bw.write(10);
        bw.flush(); 
        //fw.flush(); 
        bw.close(); 
    //  fw.close(); 


    } catch (IOException e)
    {
        e.printStackTrace();
    }

为什么每次都是覆盖result.txt呢？
我是要插入信息。。就是每次插入都放到result.txt里

[code="java"]
BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
[/code]