How to get Boolean value from Object

问题

I tried different ways to fix this, but I am not able to fix it. I am trying to get the Boolean value of an Object passed inside this method of a checkBox:

public boolean onPreferenceChange(Preference preference, Object newValue) 
{
    final String key = preference.getKey();
    referenceKey=key;
    Boolean changedValue=!(((Boolean)newValue).booleanValue()); //ClassCastException occurs here
}

I get:

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Boolean

回答1:

Instead of casting it, you can do something like

 Boolean.parseBoolean(string);

回答2:

Here's some of the source code for the Boolean class in java.

// Boolean Constructor for String types.
public Boolean(String s) {
    this(toBoolean(s));
}
// parser.
public static boolean parseBoolean(String s) {
    return toBoolean(s);
}
// ...
// Here's the source for toBoolean.
// ...
private static boolean toBoolean(String name) { 
    return ((name != null) && name.equalsIgnoreCase("true"));
}

So as you can see, you need to pass a string with the value of "true" in order for the boolean value to be true. Otherwise it's false.

assert new Boolean( "ok" ) == false; 
assert new Boolean( "True" ) == true;
assert new Boolean( "false" ) == false;

assert Boolean.parseBoolean( "ok" ) == false; 
assert Boolean.parseBoolean( "True" ) == true;
assert Boolean.parseBoolean( "false" ) == false;

回答3:

From the code you posted, and the result you are seeing, it doesn't look like newValue is a boolean. So you try to cast to a Boolean, but it's not one, so the error occurs.

It's not clear what you're trying to do. Ideally you'd make newValue a boolean. If you can't do that, this should work:

boolean newValue;
if (newValue instanceof Boolean) { 
    changedValue = newValue; // autoboxing handles this for you
} else if (newValue instanceof String) {
    changedValue = Boolean.parseBoolean(newValue);
} else { 
    // handle other object types here, in a similar fashion to above
}

Note that this solution isn't really ideal, and is somewhat fragile. In some instances that is OK, but it is probably better to re-evaluate the inputs to your method to make them a little cleaner. If you can't, then the code above will work. It's really something only you can decide in the context of your solution.

回答4:

If you know that your Preference is a CheckBoxPreference, then you can call isChecked(). It returns a boolean, not a Boolean, but that's probably close enough.

Here is some code from the APIDemos Device Administration sample (DeviceAdminSample.java).

private CheckBoxPreference mDisableCameraCheckbox;

public void onResume() {
    ...
    mDPM.setCameraDisabled(mDeviceAdminSample, mDisableCameraCheckbox.isChecked());
    ...
}

public boolean onPreferenceChange(Preference preference, Object newValue) {
...
    boolean value = (Boolean) newValue;
...
    else if (preference == mDisableCameraCheckbox) {
        mDPM.setCameraDisabled(mDeviceAdminSample, value);
        reloadSummaries();
    }
    return true;
}

来源：https://stackoverflow.com/questions/10642716/how-to-get-boolean-value-from-object

标签

java

classcastexception