Null pointer exception trying to invoke virtual method on a null object reference android studio

Question

I am trying to hide a button in my android program. I have a button with an id "btn_add" in my XML layout file. Now i want it to be invisible when the activity is opened. I am getting an error "Error trying to invoke a virtual method on a null object reference" on the line where i set the visibility to "View.INVISIBLE" when I check for errors in my logcat.

I also get the same error when i create an onlcick listener to an imageview called "like" with an id "btn_like". The following java code is responsible for that.

Your immediate help would be greatly appreciated.

Button btn_add;
ImageView like;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    btn_add=findViewById(R.id.add_product);
    btn_add.setVisibility(View.INVISIBLE);

    like = findViewById(R.id.like);

    like.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Toast.makeText(BusinessActivity.this,"liked",Toast.LENGTH_SHORT).show();

        }
    });

}}

Answer 1

This line is missing in your code below super.oncreate(). A contentView is not set. Set the contentview before accessing UI elements.

    setContentView(R.layout.your_activity_xml_layout);

Finally

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

setContentView(R.layout.your_activity_xml_layout);

btn_add=findViewById(R.id.add_product);
btn_add.setVisibility(View.INVISIBLE);

like = findViewById(R.id.like);

like.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(BusinessActivity.this,"liked",Toast.LENGTH_SHORT).show();

    }
});

}}