BAEL-4006 | Liskov Substitution Principle in Java (#9431)

* BAEL-4006 | Liskov Substitution Principle in Java

* BAEL-4006 | UNDO unintentional commit to pom.xml

* BAEL-4006 | Code review feedback implementation

* BAEL-4006 | Changes made to support the article review feedback implementation

* BAEL-4006 | Minor change to a comment

patterns/solid/src/main/java/com/baeldung/l/advanced/Account.java

@@ -0,0 +1,17 @@
+package com.baeldung.l.advanced;
+
+import java.math.BigDecimal;
+
+public abstract class Account {
+    protected abstract void deposit(BigDecimal amount);
+
+    /**
+     * Reduces the account balance by the specified amount
+     * provided given amount > 0 and account meets minimum available
+     * balance criteria.
+     *
+     * @param amount
+     */
+    protected abstract void withdraw(BigDecimal amount);
+
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/BankingAppWithdrawalService.java

@@ -0,0 +1,15 @@
+package com.baeldung.l.advanced;
+
+import java.math.BigDecimal;
+
+public class BankingAppWithdrawalService {
+    private Account account;
+
+    public BankingAppWithdrawalService(Account account) {
+        this.account = account;
+    }
+
+    public void withdraw(BigDecimal amount) {
+        account.withdraw(amount);
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/Bar.java

@@ -0,0 +1,27 @@
+package com.baeldung.l.advanced;
+
+public class Bar extends Foo {
+
+    @Override
+    // precondition: 0 < num <= 10
+    public void doStuff(int num) {
+        if (num <= 0 || num > 10) {
+            throw new IllegalArgumentException("Input out of range 1-10");
+        }
+        // some logic here...
+    }
+
+    @Override
+    // precondition: 0 < num <= 3
+    public void doOtherStuff(int num) {
+        if (num <= 0 || num > 3) {
+            throw new IllegalArgumentException("Input out of range 1-3");
+        }
+        // some logic here...
+    }
+
+    @Override
+    public Integer generateNumber() {
+        return new Integer(10);
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/Car.java

@@ -0,0 +1,26 @@
+package com.baeldung.l.advanced;
+
+public abstract class Car {
+    protected int limit;
+
+    // invariant: speed < limit;
+    protected int speed;
+
+    // Allowed to be set once at the time of creation.
+    // Value can only increment thereafter.
+    // Value cannot be reset.
+    protected int mileage;
+
+    public Car(int mileage) {
+        this.mileage = mileage;
+    }
+
+    protected abstract void turnOnEngine();
+
+    // postcondition: speed < limit
+    protected abstract void accelerate();
+
+    // postcondition: speed must reduce
+    protected abstract void brake();
+
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/CurrentAccount.java

@@ -0,0 +1,15 @@
+package com.baeldung.l.advanced;
+
+import java.math.BigDecimal;
+
+public class CurrentAccount extends Account {
+    @Override
+    protected void deposit(BigDecimal amount) {
+        // Deposit into CurrentAccount
+    }
+
+    @Override
+    protected void withdraw(BigDecimal amount) {
+        // Withdraw from CurrentAccount
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/ElectricCar.java

@@ -0,0 +1,23 @@
+package com.baeldung.l.advanced;
+
+public class ElectricCar extends Car {
+
+    public ElectricCar(int mileage) {
+        super(mileage);
+    }
+
+    @Override
+    protected void turnOnEngine() {
+        throw new AssertionError("I am an Electric Car. I don't have an engine!");
+    }
+
+    @Override
+    protected void accelerate() {
+        // this acceleration is crazy!
+    }
+
+    @Override
+    protected void brake() {
+        // Apply ElectricCar brake
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/FilePurgingJob.java

@@ -0,0 +1,18 @@
+package com.baeldung.l.advanced;
+
+import java.io.IOException;
+
+public class FilePurgingJob {
+    private FileSystem fileSystem;
+
+    public FilePurgingJob(FileSystem fileSystem) {
+        this.fileSystem = fileSystem;
+    }
+
+    public void purgeOldestFile(String path) throws IOException {
+        if (!(fileSystem instanceof ReadOnlyFileSystem)) {
+            // code to detect oldest file
+            fileSystem.deleteFile(path);
+        }
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/FileSystem.java

@@ -0,0 +1,10 @@
+package com.baeldung.l.advanced;
+
+import java.io.File;
+import java.io.IOException;
+
+public interface FileSystem {
+    File[] listFiles(String path);
+
+    void deleteFile(String path) throws IOException;
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/FixedTermDepositAccount.java

@@ -0,0 +1,15 @@
+package com.baeldung.l.advanced;
+
+import java.math.BigDecimal;
+
+public class FixedTermDepositAccount extends Account {
+    @Override
+    protected void deposit(BigDecimal amount) {
+        // Deposit into this account
+    }
+
+    @Override
+    protected void withdraw(BigDecimal amount) {
+        throw new UnsupportedOperationException("Withdrawals are not supported by FixedTermDepositAccount!!");
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/Foo.java

@@ -0,0 +1,22 @@
+package com.baeldung.l.advanced;
+
+public abstract class Foo {
+
+    // precondition: 0 < num <=5
+    public void doStuff(int num) {
+        if (num <= 0 || num > 5) {
+            throw new IllegalArgumentException("Input out of range 1-5");
+        }
+        // some logic here...
+    }
+
+    // precondition: 0 < num <=5
+    public void doOtherStuff(int num) {
+        if (num <= 0 || num > 5) {
+            throw new IllegalArgumentException("Input out of range 1-5");
+        }
+        // some logic here...
+    }
+
+    public abstract Number generateNumber();
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/HybridCar.java

@@ -0,0 +1,28 @@
+package com.baeldung.l.advanced;
+
+public class HybridCar extends Car {
+    // invariant: charge >= 0;
+    private int charge;
+
+    public HybridCar(int mileage) {
+        super(mileage);
+    }
+
+    @Override
+    protected void turnOnEngine() {
+        // Start HybridCar
+    }
+
+    @Override
+    // postcondition: speed < limit
+    protected void accelerate() {
+        // Accelerate HybridCar speed < limit
+    }
+
+    @Override
+    // postcondition: speed must reduce
+    // postcondition: charge must increase
+    protected void brake() {
+        // Apply HybridCar brake
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/MotorCar.java

@@ -0,0 +1,25 @@
+package com.baeldung.l.advanced;
+
+public class MotorCar extends Car {
+
+    public MotorCar(int mileage) {
+        super(mileage);
+    }
+
+    @Override
+    protected void turnOnEngine() {
+        // Start MotorCar
+    }
+
+    @Override
+    // postcondition: speed < limit
+    protected void accelerate() {
+        // Accelerate MotorCar
+    }
+
+    @Override
+    // postcondition: speed must reduce
+    protected void brake() {
+        // Apply MotorCar brake
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/ReadOnlyFileSystem.java

@@ -0,0 +1,16 @@
+package com.baeldung.l.advanced;
+
+import java.io.File;
+import java.io.IOException;
+
+public class ReadOnlyFileSystem implements FileSystem {
+    public File[] listFiles(String path) {
+        // code to list files
+        return new File[0];
+    }
+
+    public void deleteFile(String path) throws IOException {
+        // Do nothing.
+        // deleteFile operation is not supported on a read-only file system
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/SavingsAccount.java

@@ -0,0 +1,15 @@
+package com.baeldung.l.advanced;
+
+import java.math.BigDecimal;
+
+public class SavingsAccount extends Account {
+    @Override    
+    protected void deposit(BigDecimal amount) {
+        // Deposit into SavingsAccount
+    }
+
+    @Override
+    protected void withdraw(BigDecimal amount) {
+        // Withdraw from SavingsAccount
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/ToyCar.java

@@ -0,0 +1,24 @@
+package com.baeldung.l.advanced;
+
+public class ToyCar extends Car {
+
+    public ToyCar(int mileage) {
+        super(mileage);
+    }
+
+    protected void turnOnEngine() {
+
+    }
+
+    protected void accelerate() {
+
+    }
+
+    protected void brake() {
+
+    }
+
+    public void reset() {
+        mileage = 0;
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/refactored/Account.java

@@ -0,0 +1,7 @@
+package com.baeldung.l.advanced.refactored;
+
+import java.math.BigDecimal;
+
+public abstract class Account {
+    protected abstract void deposit(BigDecimal amount);
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/refactored/BankingAppWithdrawalService.java

@@ -0,0 +1,17 @@
+package com.baeldung.l.advanced.refactored;
+
+import com.baeldung.l.advanced.Account;
+
+import java.math.BigDecimal;
+
+public class BankingAppWithdrawalService {
+    private WithdrawableAccount withdrawableAccount;
+
+    public BankingAppWithdrawalService(WithdrawableAccount withdrawableAccount) {
+        this.withdrawableAccount = withdrawableAccount;
+    }
+
+    public void withdraw(BigDecimal amount) {
+        withdrawableAccount.withdraw(amount);
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/refactored/CurrentAccount.java

@@ -0,0 +1,13 @@
+package com.baeldung.l.advanced.refactored;
+
+import java.math.BigDecimal;
+
+public class CurrentAccount extends WithdrawableAccount {
+    protected void deposit(BigDecimal amount) {
+        // Deposit into CurrentAccount
+    }
+
+    protected void withdraw(BigDecimal amount) {
+        // Withdraw from CurrentAccount
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/refactored/FixedTermDepositAccount.java

@@ -0,0 +1,9 @@
+package com.baeldung.l.advanced.refactored;
+
+import java.math.BigDecimal;
+
+public class FixedTermDepositAccount extends Account {
+    protected void deposit(BigDecimal amount) {
+        // Deposit into this account
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/refactored/SavingsAccount.java

@@ -0,0 +1,13 @@
+package com.baeldung.l.advanced.refactored;
+
+import java.math.BigDecimal;
+
+public class SavingsAccount extends WithdrawableAccount {
+    protected void deposit(BigDecimal amount) {
+        // Deposit into SavingsAccount
+    }
+
+    protected void withdraw(BigDecimal amount) {
+        // Withdraw from SavingsAccount
+    }
+}

patterns/solid/src/main/java/com/baeldung/l/advanced/refactored/WithdrawableAccount.java

@@ -0,0 +1,14 @@
+package com.baeldung.l.advanced.refactored;
+
+import java.math.BigDecimal;
+
+public abstract class WithdrawableAccount extends Account {
+    /**
+     * Reduces the account balance by the specified amount
+     * provided given amount > 0 and account meets minimum available
+     * balance criteria.
+     *
+     * @param amount
+     */
+    protected abstract void withdraw(BigDecimal amount);
+}