Toast

import android.widget.Toast;

Toast.makeText(MainActivity.this,"ok",Toast.LENGTH_SHORT).show();

第三个参数：Toast.LENGTH_SHORT或Toast.LENGTH_LONG

全局：

Toast.makeText(getApplicationContext(), "finished!", Toast.LENGTH_SHORT).show();

子线程中：

import android.os.Handler;
import android.os.Message;

private Handler handler = new Handler() {
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        switch (msg.what) {      //判断标志位
            case 0:
                Toast.makeText(getApplicationContext(), "finished!", Toast.LENGTH_SHORT).show();
                break;
        }
    }
};

new Thread(new Runnable() {
    @Override
    public void run() {
        Message msg = new Message();
        msg.what=0;   //标志消息的标志
        handler.sendMessage(msg);
    }
}).start();

快捷代码：

    public void MakeToast(String str) {
        android.os.Message msg = new android.os.Message();
        msg.what = TOAST;
        Bundle bundle = new Bundle();
        bundle.putString("message", str);
        msg.setData(bundle);
        myhandler.sendMessage(msg);
    }

    public Handler myhandler = new Handler() {
        public void handleMessage(android.os.Message msg) {
            super.handleMessage(msg);
            switch (msg.what) {      //判断标志位
                case TOAST:
                    Toast.makeText(getApplicationContext(), msg.getData().getString("message"), Toast.LENGTH_SHORT).show();
                    break;
            }
        }
    };