Cannot fix Java null pointer error

Question

I have some code that when I run it returns a null pointer error. This is the code and error from the logcat:

import android.support.v7.app.AppCompatActivity;
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Answer 1

You are not setting the onClickListener for your red button, you are reassigning the listener to the blue button.

Button red = (Button) findViewById(R.id.red_button);
blue.setOnClickListener(new View.OnClickListener() {

Have you also defined the onClick property in the xml layout file? If so then you need to ensure you have a method matching the name you have specified. For example if you have entered

onClick="buttonClicked"

You need to define a method called

public void buttonClicked() { /* OnClick functionality here */ }

See: @https://stackoverflow.com/a/38547338/1540698 from @vucko for your second issue.