假設(shè)我們有一個名為Customer的類，它負責管理客戶的信息和交易。現(xiàn)在我們想要對這個類進行改進，讓它只負責一個職責，也就是管理客戶信息和交易。我們可以考慮采用單一職責原則，將原來的兩個職責分開，讓Customer只負責管理客戶信息，而交易職責則由另一個類Transaction來負責。

// 客戶類，負責管理客戶信息和交易  
public class Customer {  
    private String name;  
    private int age;  
    private List<Transaction> transactions;
    public Customer(String name, int age) {  
        this.name = name;  
        this.age = age;  
        this.transactions = new ArrayList<>();  
    }
    public void addTransaction(Transaction transaction) {  
        this.transactions.add(transaction);  
    }
    public void removeTransaction(Transaction transaction) {  
        this.transactions.remove(transaction);  
    }
    public String getName() {  
        return name;  
    }
    public int getAge() {  
        return age;  
    }
    public List<Transaction> getTransactions() {  
        return transactions;  
    }  
}
// 交易類，負責管理交易  
public class Transaction {  
    private String description;  
    private double amount;
    public Transaction(String description, double amount) {  
        this.description = description;  
        this.amount = amount;  
    }
    public String getDescription() {  
        return description;  
    }
    public double getAmount() {  
        return amount;  
    }  
}
// 客戶端類，演示單一職責原則的應用  
public class Client {  
    public static void main(String[] args) {  
        // 創(chuàng)建客戶對象  
        Customer customer = new Customer("John", 30);
        // 創(chuàng)建交易對象  
        Transaction transaction1 = new Transaction("Buy Coffee", 10.00);  
        Transaction transaction2 = new Transaction("Sell Stock", 50.00);
        // 添加交易到客戶對象  
        customer.addTransaction(transaction1);  
        customer.addTransaction(transaction2);
        // 獲取客戶信息和交易列表  
        String name = customer.getName();  
        int age = customer.getAge();  
        List<Transaction> transactions = customer.getTransactions();
        // 輸出客戶信息和交易列表  
        System.out.println("Customer name: " + name + ", age: " + age + ", transactions: " + transactions);  
    }  
}

在上面的代碼中，Customer類只負責管理客戶信息，它擁有了四個方法，分別是addTransaction,removeTransaction和getName,getAge。Transaction類只負責管理交易，它擁有了兩個方法，分別是getDescription和getAmount。