Cannot reference “X” before supertype constructor has been called, where x is a final variable

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The reason why the code would not initially compile is because defaultValue is an instance variable of the class Test, meaning that when an object of type Test is created, a unique instance of defaultValue is also created and attached to that particular object. Because of this, it is not possible to reference defaultValue in the constructor, as neither it, nor the object have been created yet.

The solution is to make the final variable static:

public class Test {

    private static final int defaultValue = 10;
    private int var;

    public Test() {
        this(defaultValue);
    }

    public Test(int i) {
        var = i;
    }
}

By making the variable static, it becomes associated with the class itself, rather than instances of that class and is shared amongst all instances of Test. Static variables are created when the JVM first loads the class. Since the class is already loaded when you use it to create an instance, the static variable is ready to use and so can be used in the class, including the constructor.

References:

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