在Java中如何使用内部类封装逻辑_OOP内部类使用技巧分享

public class BankAccount {
    private double balance;
    private String accountNumber;

    public BankAccount(String accountNumber, double balance) {
        this.accountNumber = accountNumber;
        this.balance = balance;
    }

    // 内部类：交易记录
    public class Transaction {
        private double amount;
        private String type; // deposit or withdrawal

        public Transaction(double amount, String type) {
            this.amount = amount;
            this.type = type;
        }

        public void apply() {
            if ("deposit".equals(type)) {
                balance += amount;
            } else if ("withdrawal".equals(type) && balance >= amount) {
                balance -= amount;
            }
        }

        public String getSummary() {
            return type + " " + amount + ", new balance: " + balance;
        }
    }

    public Transaction createTransaction(double amount, String type) {
        return new Transaction(amount, type);
    }
}

public class UserForm {
    private String email;
    private String password;

    public UserForm(String email, String password) {
        this.email = email;
        this.password = password;
    }

    // 私有内部类：负责验证逻辑
    private class Validator {
        public boolean isValid() {
            return isEmailValid() && isPasswordValid();
        }

        private boolean isEmailValid() {
            return email != null && email.contains("@");
        }

        private boolean isPasswordValid() {
            return password != null && password.length() >= 6;
        }
    }

    public boolean validate() {
        return new Validator().isValid();
    }
}
</font>
</p>外部无法创建 Validator 实例，避免了验证逻辑被误用或绕过，提升了安全性。</p>

<H3>局部内部类与匿名内部类：简化短期逻辑</H3>
<p>如果某个类只在方法内部使用一次，可以考虑使用局部内部类或匿名内部类。</p>
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<p>例如，在处理事件监听时：</p>
<font color="#0000CC">
<pre class="brush:php;toolbar:false;">
public class Button {
    public void onClick() {
        // 匿名内部类实现点击行为
        ActionListener listener = new ActionListener() {
            @Override
            public void actionPerformed() {
                System.out.println("Button clicked!");
            }
        };
        listener.actionPerformed();
    }

    interface ActionListener {
        void actionPerformed();
    }
}
</font>
<p>这种方式避免了创建额外的顶层类，让代码更紧凑，尤其适用于回调场景。</p>

<H3>静态内部类：独立但逻辑相关</H3>
<p>使用 <strong>static</strong> 修饰的内部类不依赖外部类实例，适合存放与外部类相关但无需访问其实例成员的工具逻辑。</p>
<p>例如，定义一个配置工具类：</p>
<font color="#0000CC">
<pre class="brush:php;toolbar:false;">
public class DatabaseManager {
    private String host;
    private int port;

    // 静态内部类：配置构建器
    public static class Config {
        private String host = "localhost";
        private int port = 5432;

        public Config setHost(String host) {
            this.host = host;
            return this;
        }

        public Config setPort(int port) {
            this.port = port;
            return this;
        }

        public DatabaseManager build() {
            return new DatabaseManager(host, port);
        }
    }

    private DatabaseManager(String host, int port) {
        this.host = host;
        this.port = port;
    }
}
</font>
<p>调用方式简洁：</p>
<font color="#0000CC">
<pre class="brush:php;toolbar:false;">
DatabaseManager db = new DatabaseManager.Config()
    .setHost("192.168.1.100")
    .setPort(3306)
    .build();