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    <p>There is no way in Java to be notified when a variable or class field changes. What you need to do is to implement a simple wrapper class for your int so that clients can register for callbacks whenever the value changes. This class might look something like this:</p> <pre><code>package com.example.android; /** * A store of an int value. You can register a listener that will be notified * when the value changes. */ public class IntValueStore { /** * The current value. */ int mValue; /** * The listener (you might want turn this into an array to support many * listeners) */ private IntValueStoreListener mListener; /** * Construct a the int store. * * @param initialValue The initial value. */ public IntValueStore(int initialValue) { mValue = initialValue; } /** * Sets a listener on the store. The listener will be modified when the * value changes. * * @param listener The {@link IntValueStoreListener}. */ public void setListener(IntValueStoreListener listener) { mListener = listener; } /** * Set a new int value. * * @param newValue The new value. */ public void setValue(int newValue) { mValue = newValue; if (mListener != null) { mListener.onValueChanged(mValue); } } /** * Get the current value. * * @return The current int value. */ public int getValue() { return mValue; } /** * Callbacks by {@link IntValueModel}. */ public static interface IntValueStoreListener { /** * Called when the value of the int changes. * * @param newValue The new value. */ void onValueChanged(int newValue); } } </code></pre> <p>Now you need to have some class that implements the IntValueStoreListener interface. You could let that be the <code>Activity</code>, which would then keep track of a <code>TextView</code> to update. I would implement a trivial custom <code>TextView</code> instead, like this:</p> <pre><code>package com.example.android; import com.example.android.IntValueStore.IntValueStoreListener; import android.content.Context; import android.util.AttributeSet; import android.widget.TextView; public class IntTextView extends TextView implements IntValueStoreListener{ public IntTextView(Context context) { super(context); } public IntTextView(Context context, AttributeSet attrs) { super(context, attrs); } public void onValueChanged(int newValue) { // The int got a new value! Update the text setText(String.valueOf(newValue)); } } </code></pre> <p>You can now setup your layout XML. For example:</p> <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt; &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" &gt; &lt;Button android:id="@+id/btn_increment" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Increment" /&gt; &lt;Button android:id="@+id/btn_double" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Double" /&gt; &lt;com.example.android.IntTextView android:id="@+id/text_current_value" android:layout_width="match_parent" android:layout_height="wrap_content" /&gt; &lt;/LinearLayout&gt; </code></pre> <p>An activity that does the necessary setup would look like this:</p> <pre><code>package com.example.android; import android.app.Activity; import android.os.Bundle; import android.view.View; public class IntValueStoreActivity extends Activity { private IntValueStore mIntValueModel = new IntValueStore(1); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Initialize the text view with the initial value IntTextView intTextView = (IntTextView)findViewById(R.id.text_current_value); intTextView.setText(String.valueOf(mIntValueModel.getValue())); // Setup the text view as a listener so it gets updated whenever the int // value changes mIntValueModel.setListener(intTextView); // Setup an OnClickListener that will increment the int value by 1. The // TextView will be automatically updated since it is setup as a // listener to the int value store findViewById(R.id.btn_increment).setOnClickListener(new View.OnClickListener() { public void onClick(View view) { mIntValueModel.setValue(mIntValueModel.getValue() + 1); } }); // Setup an OnClickListener that will double the int value. The TextView // will be automatically updated since it is setup as a listener to the // int value store findViewById(R.id.btn_double).setOnClickListener(new View.OnClickListener() { public void onClick(View view) { mIntValueModel.setValue(mIntValueModel.getValue() * 2); } }); } } </code></pre> <p>This will give you the following UI:</p> <p><img src="https://i.stack.imgur.com/n4fWH.png" alt="App screenshot"></p> <p>Whenever you click any of the buttons, the <code>TextView</code> will almost magically update the value it displays, even though none of the OnClickListeners have any code to touch the <code>TextView</code>!</p> <p>This is actually a common pattern in programming called <a href="http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller" rel="noreferrer">Model-view-controller</a>. In the sample code above, the Model is <code>IntValueStore</code> and the View is <code>IntTextView</code> and there is no Controller.</p>
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