Androidはアカウントのパスワードを覚える機能を実現します。

<CheckBox
    android:id="@+id/checkbox"
    android:radius="5dp"
    android:text="   "
    android:layout_marginLeft="20dp"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

 private CheckBox checkBox;

 @Override
 protected void onCreate(Bundle savedInstanceState) {

  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  checkBox = findViewById(R.id.checkbox);
  SharedPreferences sp = getSharedPreferences("items",MODE_PRIVATE);

  /**
   * getBoolean(name,defaultValue)    name,   defaultValue
   *      ， flag true，    
   */
  if( sp.getBoolean("flag",false)==true ){
   getData();
   //    
   checkBox.performClick();
  }

  //  checkbox     
  checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
   @Override
   public void onCheckedChanged(CompoundButton compoundButton, boolean isCheck) {

    //   ，     ，  ，    
    if(isCheck){
     saveData();
     Toast.makeText(MainActivity.this,"   ",Toast.LENGTH_LONG).show();
    }
    else{
     clearData();
    }
   }
  });
 }
  /**
  * SharedPreferences         
  * Context.MODE_PRIVATE:       ,          ,         。
  *      ,              
  *     :Device File Explorer（idea  Android studio   ）
  * data/data/     /shared_prefs
  */
 //    
 private void clearData() {
  SharedPreferences sp = getSharedPreferences("items",MODE_PRIVATE);
  SharedPreferences.Editor editor = sp.edit();
  editor.clear();
  editor.commit();
  et1.setText("");
  et2.setText("");
 }
 /**
  *   SharedPreferences  
  */
 private void getData(){
  SharedPreferences sp = getSharedPreferences("items", Context.MODE_PRIVATE);
  String username = sp.getString("username","");
  String password = sp.getString("password","");
  et1.setText(username);

  //    
  TransformationMethod method = PasswordTransformationMethod.getInstance();
  et2.setText(password);
  et2.setTransformationMethod(method);

 }

 /**
  *    
  * android:onClick            public
  */
 public void saveData(){


  SharedPreferences sharedPreferences = getSharedPreferences("items", Context.MODE_PRIVATE);
  SharedPreferences.Editor editor = sharedPreferences.edit();

  String username = et1.getText().toString();
  String password = et2.getText().toString();

  if(!username.equals("") && !password.equals("")) {

   editor.putString("username", username);
   editor.putString("password", password);
   editor.putBoolean("flag", true); //   
   editor.commit();
  }

 }
}