如何在不改变父类变量本身的情况下改变在子类的父类中定义的变量？

class ParentClass {
    protected int variable;

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

    public int getVariable() {
        return variable;
    }
}

class ChildClass extends ParentClass {
    private int variable;

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

    public int getChildVariable() {
        return variable;
    }

    public int getParentVariable() {
        return super.getVariable();
    }
}

public class Main {
    public static void main(String[] args) {
        ParentClass parent = new ParentClass(10);
        ChildClass child = new ChildClass(20, 30);

        System.out.println("Parent Variable: " + parent.getVariable());
        System.out.println("Child Variable: " + child.getChildVariable());
        System.out.println("Parent Variable in Child: " + child.getParentVariable());
    }
}

Parent Variable: 10
Child Variable: 30
Parent Variable in Child: 20