android环境搭建好了，新建个android工程就有错,该怎么处理

package Default;import android.R;import android.app.Activity;import android.os.Bundle;public class JustTestActivity extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                这一句的main有错，说什么没有声明main这个field    }}