SOLID PRINCIPLES: Liskov Substitution Principle 🪆🔃

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SOLID PRINCIPLES: Liskov Substitution Principle 🪆🔃

· java

SOLID principles basically form the fundamental guidelines for building 

👉 object-oriented , 

👉 loosely coupled , 

👉 robust, maintainable and 

👉 easily understandable applications .

𝐃𝐞𝐫𝐢𝐯𝐞𝐝 𝐜𝐥𝐚𝐬𝐬𝐞𝐬 𝐦𝐮𝐬𝐭 𝐛𝐞 𝐬𝐮𝐛𝐬𝐭𝐢𝐭𝐮𝐭𝐚𝐛𝐥𝐞 🔃 𝐟𝐨𝐫 𝐭𝐡𝐞 𝐛𝐚𝐬𝐞 𝐜𝐥𝐚𝐬𝐬.

In simple words, If class A is extending class B, we should be able to replace B with A, without disrupting the behavior of our program.

As per OOPS concepts inheritance 🪆 is a good practice but Liskov principle mandates to use inheritance with a careful ⚠️ consideration.

We should only use inheritance if our super class is replaceable 🔃 with a sub class in all the instances.

For ex: Classic Square Rectangle problem.

public class Rectangle {
    private double height;
    private double width;
    public void setHeight(double h) { height = h; }
    public void setWidht(double w) { width = w; }
//getters and calculateArea method
}
public class Square extends Rectangle {
    public void setHeight(double h) {
        super.setHeight(h);
        super.setWidth(w);
    }
    public void setWidth(double h) {
        super.setHeight(h);
        super.setWidth(w);
    }
}

𝐀𝐬 𝐢𝐭𝐬 𝐜𝐥𝐞𝐚𝐫 𝐛𝐚𝐬𝐞 𝐜𝐥𝐚𝐬𝐬 𝐑𝐞𝐜𝐭𝐚𝐧𝐠𝐥𝐞 𝐢𝐬 𝐜𝐥𝐞𝐚𝐫𝐥𝐲 𝐧𝐨𝐭 𝐫𝐞𝐩𝐥𝐚𝐜𝐞𝐚𝐛𝐥𝐞 𝐛𝐲 𝐬𝐮𝐛 𝐜𝐥𝐚𝐬𝐬 𝐒𝐪𝐮𝐚𝐫𝐞 , 𝐚𝐬 𝐬𝐪𝐮𝐚𝐫𝐞 𝐡𝐚𝐬 𝐚 𝐜𝐨𝐧𝐬𝐭𝐫𝐚𝐢𝐧𝐭 𝐨𝐟 𝐞𝐪𝐮𝐚𝐥 𝐡𝐞𝐢𝐠𝐡𝐭 𝐚𝐧𝐝 𝐰𝐢𝐝𝐭𝐡,

𝐬𝐨 𝐬𝐮𝐛𝐬𝐭𝐢𝐭𝐮𝐭𝐢𝐧𝐠 𝐑𝐞𝐜𝐭𝐚𝐧𝐠𝐥𝐞 𝐜𝐥𝐚𝐬𝐬 𝐰𝐢𝐭𝐡 𝐒𝐪𝐮𝐚𝐫𝐞 𝐜𝐥𝐚𝐬𝐬 𝐛𝐫𝐞𝐚𝐤𝐬 𝐋𝐒𝐏.