可藉由 HideReturnsTransformationMethod 物件來轉換明碼 以及 PasswordTransformationMethod 物件來轉換成暗碼
建立物件後再呼叫 EditText 的 setTransformationMethod(), 傳入剛剛產生的物件即可完成轉換
Source Code

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.text.method.HideReturnsTransformationMethod;
import android.text.method.PasswordTransformationMethod;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.CompoundButton.OnCheckedChangeListener;
import android.widget.EditText;
public class MainActivity extends ActionBarActivity
{
    private EditText mInputPassword;
    private CheckBox mShowPassword;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initLayoutComponents();
    }
    private void initLayoutComponents()
    {
        mInputPassword = (EditText) findViewById(R.id.password);
        mShowPassword = (CheckBox) findViewById(R.id.switchPassword);
        mShowPassword.setOnCheckedChangeListener(new OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked)
            {
                if (isChecked) {
                    mInputPassword.setTransformationMethod(new HideReturnsTransformationMethod());
                } else {
                    mInputPassword.setTransformationMethod(new PasswordTransformationMethod());
                }
            }
        });
    }
}

第33行及35行即為轉換的過程
 
R.layout.activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.changepasswordtostar.MainActivity" >
    <EditText
        android:id="@+id/password"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="@string/input_password_hint"
        android:inputType="textPassword"/>
    <CheckBox
        android:id="@+id/switchPassword"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/password"
        android:layout_alignLeft="@+id/password"
        android:text="@string/showPasswrod"/>
</RelativeLayout>