package com.itheima.coolweather;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toast.makeText(this, "今天是个好天气", Toast.LENGTH_SHORT).show();
        
    }
}

package com.itheima.coolweather;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toast.makeText(this, "今天是个好天气", Toast.LENGTH_SHORT).show();
        //another change
        Toast.makeTest(thsi,"刘德华",Toast.LENGTH_LONG).show();
        
    }
}

Create MainActivity.java