Testing android:text produces different results depending if it has been modified

Question

I'm experiencing this on my code and I cannot figure out why. Basically I'm setting android:text to "0" on XML and when checking with getText if it's "0" it returns false. If I set it to 0 with setText and check again it returns true.

    <TextView android:id="@+id/edit_text"
        android:text="0" />

    TextView calc = (TextView) findViewById(R.id.edit_text);
    return( calc.getText() == "0" ); // false
    ----
    calc.setText( "0" );
    return( calc.getText() == "0" ); // true

Why does this happen? How can I check if calc.getText() is 0?

Answer 1

You never compare Objects (String are a subclass of CharSequence which is a subclass of Object, and I'd recommend working with them instead of CharSequence) with ==, since that compares references, not actual Object content. All Objects have a equals() method, but Strings defintely customize it (override) to implement a check for if the Strings to compare are the same.

Instead do calc.getText().toString().equals ("0");

So in terms of why it's happening - Android makes one Object then when you specify "0", you create another one. Using equals() solves this because it checks the content first then gives a result (true/false).