Intent in = new Intent(getApplicationContext(),SecondaryScreen.class);    
    startActivity(in);

    This is an explicit intent to start secondscreen activity.

    Intent in = new Intent(getApplicationContext(),SecondaryScreen.class);    
    startActivity(in);

    This is an explicit intent to start secondscreen activity.

Intent iinent= new Intent(Homeactivity.this,secondactivity.class);
startActivity(iinent);

Intent i = new Intent(firstactivity.this, secondactivity.class);
startActivity(i);

虽然已经提供了正确的答案，但我在这里搜索语言Kotlin的答案。这个问题不是关于特定于语言的，所以我添加代码来完成这个任务在Kotlin语言。

下面是如何在Kotlin中为andorid做到这一点

testActivityBtn1.setOnClickListener{
      val intent = Intent(applicationContext,MainActivity::class.java)
      startActivity(intent)

 }

Button button = findViewById(R.id.button);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(SplashActivity.this,HomeActivity.class);
            startActivity(intent);
        }
    });