Editing Bridge pattern (section)

=== Java ===
The following [[Java (programming language)|Java]] program defines a bank account that separates the account operations from the logging of these operations. 

<syntaxhighlight lang="java">
// Logger has two implementations: info and warning
@FunctionalInterface
interface Logger {
    void log(String message);
    
    static Logger info() {
        return message -> System.out.println("info: " + message);
    }
    static Logger warning() {
        return message -> System.out.println("warning: " + message);
    }
}

abstract class AbstractAccount {
    private Logger logger = Logger.info();
    
    public void setLogger(Logger logger) {
        this.logger = logger;
    }
    
    // the logging part is delegated to the Logger implementation
    protected void operate(String message, boolean result) {
        logger.log(message + " result " + result);
    }
}

class SimpleAccount extends AbstractAccount {
    private int balance;
    
    public SimpleAccount(int balance) {
        this.balance = balance;
    }
    
    public boolean isBalanceLow() {
        return balance < 50;
    }
    
    public void withdraw(int amount) {
        boolean shouldPerform = balance >= amount;
        if (shouldPerform) {
            balance -= amount;
        }
        operate("withdraw " + amount, shouldPerform);
    }
}

public class BridgeDemo {
    public static void main(String[] args) {
        SimpleAccount account = new SimpleAccount(100);
        account.withdraw(75);
        
        if (account.isBalanceLow()) {
            // you can also change the Logger implementation at runtime
            account.setLogger(Logger.warning());
        }
        
        account.withdraw(10);
        account.withdraw(100);
    }
}
</syntaxhighlight>

It will output:
<pre>
info: withdraw 75 result true
warning: withdraw 10 result true
warning: withdraw 100 result false
</pre>