Typedef Annotations: @IntDef, @StringDef

IntDef Annotations

This annotation (opens new window) ensures that only the valid integer constants that you expect are used.
The following example illustrates the steps to create an annotation:

import android.support.annotation.IntDef;

public abstract class Car {

    //Define the list of accepted constants
    @IntDef({MICROCAR, CONVERTIBLE, SUPERCAR, MINIVAN, SUV})

    //Tell the compiler not to store annotation data in the .class file
    @Retention(RetentionPolicy.SOURCE)
    //Declare the CarType annotation
    public @interface CarType {}

    //Declare the constants
    public static final int MICROCAR = 0;
    public static final int CONVERTIBLE = 1;
    public static final int SUPERCAR = 2;
    public static final int MINIVAN = 3;
    public static final int SUV = 4;

    @CarType
    private int mType;

    @CarType
    public int getCarType(){
        return mType;
    };

    public void setCarType(@CarType int type){
        mType = type;
    }
}

They also enable code completion to automatically offer the allowed constants.
When you build this code, a warning is generated if the type parameter does not reference one of the defined constants.

Combining constants with flags

Using the IntDef#flag() attribute set to true, multiple constants can be combined.

Using the same example (opens new window) in this topic:

public abstract class Car {

    //Define the list of accepted constants
    @IntDef(flag=true, value={MICROCAR, CONVERTIBLE, SUPERCAR, MINIVAN, SUV})

    //Tell the compiler not to store annotation data in the .class file
    @Retention(RetentionPolicy.SOURCE)

    .....

}

Users can combine the allowed constants with a flag (such as |, &, ^ ).

Remarks

The annotations package includes a number of useful metadata annotations you can decorate your own code with, to help catch bugs.

Just add the dependency in the build.gradle file.

dependencies {
    compile 'com.android.support:support-annotations:25.3.1'
}