Using keys for passing values between activities
The keys of the 2 extras are "com.example.testapp.num1" and "com.example.testapp.num2", so you must use these to retrieve them and not "num1" and "num2":
if (getIntent().hasExtra("com.example.testapp.num1") && getIntent().hasExtra("com.example.testapp.num2")){
int num1=getIntent().getExtras().getInt("com.example.testapp.num1");
int num2=getIntent().getExtras().getInt("com.example.testapp.num2");
TextView bigger=findViewById(R.id.biggerNView);
bigger.setText(String.valueOf(Math.max(num1,num2)));
}