任何客戶端都不應被迫依賴它不使用的方法

考慮辦公空間的範例，其中使用物件表示各種輸出設備

介面隔離原則之前：

I多功能介面

/**
 * @ImultiFunction interface has methods related to all output devices present in office space
 * for devices like Printer, Scanner, Fax machines, etc
*/
public interface IMultiFunction {
    public void print();
    public void getPrintSpoolDetails();
    public void scan();
    public void scanPhoto();
    public void fax();
    public void internetFax();
}

現在為各種設備實現上述通用介面

XeroxWorkCenter 類別具有所有功能

/**
 * 
 * You must have seen Xerox work station device which has all the features in one like printing, scanning, xerox,
 * fax etc
*/
public class XeroxWorkCenter implements IMultiFunction {

    @Override
    public void print() {
        // real printing code
    }

    @Override
    public void getPrintSpoolDetails() {
        // real get print spool details code
    }

    @Override
    public void scan() {
        // read scanning code
    }

    @Override
    public void scanPhoto() {
        // real scan photo code 
    }

    @Override
    public void fax() {
        // real fax code
    }

    @Override
    public void internetFax() {
        // real internet fax code
    }

}

HpPrinterNScanner 類別具有列印和掃描功能

public class HpPrinterNScanner implements IMultiFunction {

    @Override
    public void print() {
        // real printing code
    }

    @Override
    public void getPrintSpoolDetails() {
        // real get print spool details code
    }

    @Override
    public void scan() {
        // read scanning code
    }

    @Override
    public void scanPhoto() {
        // real scan photo code 
    }

    //Since HpPrinterNScanner has only printing and scanning abilities fax() and internetFax() will have empty body
    @Override
    public void fax() {}

    @Override
    public void internetFax() {}

}

CanonPrinter 類別僅具有列印功能

public class CanonPrinter implements IMultiFunction {

    @Override
    public void print() {
        // real printing code
    }

    @Override
    public void getPrintSpoolDetails() {
        // real get print spool details code
    }

    //Since the CanonPrinter has only printing ability rest of the method will have an empty body
    @Override
    public void scan() {}

    @Override
    public void scanPhoto() {}

    @Override
    public void fax() {}

    @Override
    public void internetFax() {}

}

ISP違規辨識技術

• 胖介面（具有兩個多個方法聲明的介面）
• 低內聚的介面（具有不太可能彼此相關的方法的介面）
• *空方法實作*（當類別被迫實作它們不使用的方法時，它們會將方法的實作留空）

後介面隔離原則：

public interface IPrint {
    public void print();
    public void getPrintSpoolDetails();
}

public interface IScan {
    public void scan();
    public void scanPhoto();
}

public interface IFax {
    public void fax();
    public void internetFax();
}

/**
 * 
 * You must have seen the Xerox workstation device which has all the features in one like printing, scanning, xerox, fax, etc.
*/
public class XeroxWorkCenter implements IPrint,IScan,IFax {

    @Override
    public void print() {
        // real printing code
    }

    @Override
    public void getPrintSpoolDetails() {
        // real get print spool details code
    }

    @Override
    public void scan() {
        // read scanning code
    }

    @Override
    public void scanPhoto() {
        // real scan photo code ̰
    }

    @Override
    public void fax() {
        // real fax code
    }

    @Override
    public void internetFax() {
        // real internet fax code
    }

}

public class HpPrinterNScanner implements IPrint,IScan {

    @Override
    public void print() {
        // real printing code
    }

    @Override
    public void getPrintSpoolDetails() {
        // real get print spool details code
    }

    @Override
    public void scan() {
        // read scanning code
    }

    @Override
    public void scanPhoto() {
        // real scan photo code 
    }
}

public class CanonPrinter implements IPrint {

    @Override
    public void print() {
        // real printing code
    }

    @Override
    public void getPrintSpoolDetails() {
        // real get print spool details code
    } 
}

每個介面都有單一的職責，現在更乾淨。

ISP 與其他 SOLID 原則的關係

單一職責
將介面分割成不同的介面後，現在所有介面（如 IPrint、IScan）都有一個單一的職責

里氏替換
由於隔離，現在所有類別（實現介面）都遵循里氏替換，因為所有子類型或實作類別都可以替換為其介面引用變數