Android 添加Button事件

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);

         View btn1 = findViewById(R.id.button1);
         btn1.setOnClickListener(new ButtonClickListener());

    }

private class ButtonClickListener implements View.OnClickListener{  

          public void onClick(View v) {
              System.out.println("--click-----");

          }
    }