对话框：
new AlertDialog.Builder(MainActivity.this).setTitle("标题").setMessage("消息框").setNeutralButton("中性",null).setPositiveButton("确定", null).setNegativeButton("取消",null).show();

AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
builder.setTitle("标题");
builder.setMessage("消息框");
builder.setNeutralButton("中性",
new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {
        finish();
    }
});
builder.setPositiveButton("确定", null);
builder.setNegativeButton("取消",null);
builder.show();


提示：
Toast.makeText(Register.this, "提示", Toast.LENGTH_SHORT).show();