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**Proxy** is a **structural pattern** that creates a **substitute object** controlling access to another object.
It behaves **the same way as the original**, but can **add extra behavior**, such as caching, security, logging, or lazy loading.

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### 1. **The Core Idea**

The client does not work with the real object but with its "representative", the proxy.
This proxy **intercepts calls** and decides whether to forward them to the real object or handle them itself.

> In simple terms: Proxy is a "smart reference" to the real object.

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### 2. **When It Is Used**

- **Access control** - checking permissions before reaching a resource.
- **Lazy initialization** - the object is created only on first use.
- **Remote access (Remote Proxy)** - reaching an object on another server.
- **Caching** - storing call results for reuse.
- **Protection or logging** - adding layers of security or analytics.

---

### 3. **Example (Java)**

```java
interface Image {
    void display();
}

class RealImage implements Image {
    private String fileName;

public RealImage(String fileName) {
        this.fileName = fileName;
        loadFromDisk();
    }

private void loadFromDisk() {
        System.out.println("Loading: " + fileName);
    }

public void display() {
        System.out.println("Displaying: " + fileName);
    }
}

class ProxyImage implements Image {
    private RealImage realImage;
    private String fileName;

public ProxyImage(String fileName) {
        this.fileName = fileName;
    }

public void display() {
        if (realImage == null) realImage = new RealImage(fileName);
        realImage.display();
    }
}
```

**Usage:**

```java
Image img = new ProxyImage("photo.jpg");
img.display(); // loads on the first call
img.display(); // no loading the second time
```

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### 4. **Advantages**

- Controls and optimizes access to heavy or remote resources.
- Lazy initialization saves memory and time.
- Lets you add functionality without changing the original class.

---

### 5. **Conclusion**

**Proxy** is an intermediary object that **substitutes for the real object**,
intercepts access to it, and **controls access, execution, or caching**,
while staying **transparent and interface-compatible** for the client.

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