MainActivity.java

package com.travis.q2orderui;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    private TextView numberView;
    private int order = 0;
    Button minusButton;
    Button plusButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        numberView = (TextView) findViewById(R.id.order_number);

        Button minusButton = (Button) findViewById(R.id.minus_button);
        minusButton.setOnClickListener(this);

        Button plusButton = (Button) findViewById(R.id.plus_button);
        plusButton.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        int id = v.getId();
        switch (id) {
            case R.id.minus_button:
                if (order > 0) order--;
                break;
            case R.id.plus_button:
                order++;
                break;
            default:
                return;
        }
        numberView.setText(String.valueOf(order));
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


}