如何将父类中的变量发送给子自定义类

class ParentClass {
    protected int parentVariable;

    public ParentClass(int parentVariable) {
        this.parentVariable = parentVariable;
    }
}

class ChildClass extends ParentClass {
    private int childVariable;

    public ChildClass(int parentVariable, int childVariable) {
        super(parentVariable);
        this.childVariable = childVariable;
    }

    public void printVariables() {
        System.out.println("Parent Variable: " + parentVariable);
        System.out.println("Child Variable: " + childVariable);
    }
}

public class Main {
    public static void main(String[] args) {
        ChildClass child = new ChildClass(10, 20);
        child.printVariables();
    }
}