singleton added

Author: maciej-nowak

singleton/README.md

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+# Singleton
+This is repository of http://androidcode.pl blog. It shows uses of Singleton in Android. It is a part of Design Patterns - Singleton post in the blog.

singleton/example/DetailsActivity.java

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+public class DetailsActivity extends AppCompatActivity {
+
+    private TextView name, age, isStudent;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_details);
+
+        name = findViewById(R.id.name);
+        age = findViewById(R.id.age);
+        isStudent = findViewById(R.id.isStudent);
+
+        initValues();
+    }
+
+    private void initValues() {
+        name.setText(SharedPref.getInstance(this).readString(SharedPref.NAME_KEY));
+        age.setText(String.valueOf(SharedPref.getInstance(this).readInt(SharedPref.AGE_KEY)));
+        isStudent.setText(String.valueOf(SharedPref.getInstance(this).readBoolean(SharedPref.STUDENT_KEY)));
+    }
+}

singleton/example/MainActivity.java

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+public class MainActivity extends AppCompatActivity {
+
+    private Button clearPref, setPref, showDetails;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_main);
+
+        clearPref = findViewById(R.id.clear_preferences);
+        setPref = findViewById(R.id.default_preferences);
+        showDetails = findViewById(R.id.show_details);
+
+        clearPref.setOnClickListener(v -> clearPreferences());
+        setPref.setOnClickListener(v -> setDefaultPreferences());
+        showDetails.setOnClickListener(v -> showPreferences());
+    }
+
+    private void clearPreferences() {
+        SharedPref.getInstance(getApplicationContext()).clearPreferences();
+    }
+
+    private void setDefaultPreferences() {
+        SharedPref.getInstance(getApplicationContext()).writeString(SharedPref.NAME_KEY, "Maciej");
+        SharedPref.getInstance(getApplicationContext()).writeInt(SharedPref.AGE_KEY, 26);
+        SharedPref.getInstance(getApplicationContext()).writeBoolean(SharedPref.STUDENT_KEY, false);
+    }
+
+    private void showPreferences() {
+        Intent intent = new Intent(this, DetailsActivity.class);
+        startActivity(intent);
+    }
+}

singleton/example/SharedPref.java

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+public class SharedPref {
+
+    public static final String NAME_KEY = "NAME";
+    public static final String AGE_KEY = "AGE";
+    public static final String STUDENT_KEY = "IS_STUDENT";
+
+    private static SharedPref instance;
+    private static SharedPreferences sharedPreferences;
+    private static SharedPreferences.Editor editor;
+
+    private SharedPref() {
+    }
+
+    public static SharedPref getInstance(Context context) {
+        if(instance == null) {
+            synchronized (SharedPref.class) {
+                if(instance == null) {
+                    instance = new SharedPref();
+                    sharedPreferences = context.getSharedPreferences(context.getPackageName(), Activity.MODE_PRIVATE);
+                    editor = sharedPreferences.edit();
+                }
+            }
+        }
+        return instance;
+    }
+
+    public void writeString(String key, String value) {
+        editor.putString(key, value);
+        editor.commit();
+    }
+
+    public void writeInt(String key, int value) {
+        editor.putInt(key, value);
+        editor.commit();
+    }
+
+    public void writeBoolean(String key, boolean value) {
+        editor.putBoolean(key, value);
+        editor.commit();
+    }
+
+    public String readString(String key) {
+        return sharedPreferences.getString(key, "");
+    }
+
+    public int readInt(String key) {
+        return sharedPreferences.getInt(key, 0);
+    }
+
+    public boolean readBoolean(String key) {
+        return sharedPreferences.getBoolean(key, false);
+    }
+
+    public void clearPreferences() {
+        editor.clear();
+        editor.commit();
+    }
+}

singleton/pattern/DoubleCheckSingleton.java

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+public class DoubleCheckSingleton {
+
+    private static DoubleCheckSingleton INSTANCE;
+
+    private DoubleCheckSingleton() {
+    }
+
+    public static DoubleCheckSingleton getInstance() {
+        if (INSTANCE == null)
+            synchronized (DoubleCheckSingleton.class) {
+                if (INSTANCE == null)
+                    INSTANCE = new DoubleCheckSingleton();
+            }
+        return INSTANCE;
+    }
+}

singleton/pattern/Singleton.java

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+public class Singleton {
+
+    private static Singleton INSTANCE;
+
+    private Singleton() {
+    }
+
+    public static Singleton getInstance() {
+        if(INSTANCE == null) {
+            INSTANCE = new Singleton();
+        }
+        return INSTANCE;
+    }
+}

singleton/pattern/SingletonHolder.java

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+public class SingletonHolder {
+
+    private SingletonHolder() {
+    }
+
+    private static class Holder {
+        private static final SingletonHolder INSTANCE = new SingletonHolder();
+    }
+
+    public static SingletonHolder getInstance() {
+        return Holder.INSTANCE;
+    }
+}