Pemrograman Lanjut Interface
PTIIK - 2014
Objectives
Interfaces Defining an Interface How a class implements an interface Public interfaces Implementing multiple interfaces Extending an interface
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Introduction Java has single inheritance, only. This means that a child class inherits from only one parent class. Usually this is all you need. But sometimes multiple inheritance would be convenient. Interfaces give Java some of the advantages of multiple inheritance without the disadvantages. Interfaces are crucial to GUI programming
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Interface An interface describes aspects of a class other than those that it inherits from its parent. An interface is a set of requirements that the class must implement. An interface is a list of constants and method declarations. The method declarations DO NOT include an implementation (there is no method body). A class that implements an interface must implement each of the methods listed in the interface.
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Interface A class can extend one parent class to inherit the methods and instance variables of that parent. A class can also implement an interface to gain additional methods and constants. However, the additional methods must be explicitly written as part of the class definition. The interface is a list of requirements that the class definition must explicitly meet (through code, not through inheritance).
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Interface Definition An interface definition looks like this:
A method declaration is simply an access modifier, a return type, and a method signature followed by a semicolon. This looks somewhat like a class definition. But no objects can be constructed from it.
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Objects can be constructed from a class that implements an interface. A class implements an interface by doing this:
A class always extends just one parent but may implement several interfaces.
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Example interface
A method in an interface cannot be made private. A method in an interface is public by default. The constants in an interface are public static final by default.
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The second interface (default) is the preferred way to define an interface. The defaults are assumed and not explicitly coded. A class that implements an interface must implement each method in the interface. Methods from the interface must be declared public in the class. Constants from the interface can be used as if they had been defined in the class. Constants should not be redefined in the class.
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Inspect the interface. Is it correct?
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Implementing an Interface A class definition must always extend one parent, but it can implement zero or more interfaces:
The body of the class definition is the same as always. However, since it implements an interface the body must have a definition of each of the methods declared in the interface.
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Implementing an Interface The class definition can use access modifiers as usual. Here is a class definition that implements three interfaces:
Now BigClass must provide a method definition for every method declared in the three interfaces.
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Implementing an Interface Here is another class definition:
Any number of classes can implement the same interfaces.
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Interface as a Type An interface can be used as a data type for a reference variable. Since Toy and Book implement Taxable, they can both be used with a reference variable of type Taxable:
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Public Interfaces It is OK if two interfaces ask for the same method. A class that implements both interfaces only needs to provide one complete method definition to satisfy both interfaces. An interface can be made public. In fact, this is usually what is done. A public interface can be implemented by any class in any file. Many graphical user interface components implement public interfaces. You must use them to work with the GUI features of Java.
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Hierarchy of Interfaces An interface can be an extension of another interface (but not an extension of a class) A complex hierarchy of interfaces can be constructed using this feature. This is an advanced feature which you will probably not need to use.
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Hierarchy of Interfaces Contohnya, misal kita punya dua interface StudentInterface dan PersonInterface. Jika StudentInterface meng-extend PersonInterface, maka ia akan mewariskan semua deklarasi method dalam PersonInterface
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Interface vs. Abstract Class Method interface tidak punya tubuh Sebuah interface hanya dapat mendefinisikan konstanta dan abstract method Interface tidak langsung mewariskan hubungan dengan class “istimewa” lainnya, mereka didefinisikan secara independent.
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Interface vs. Class
Bagaimanapun, Anda tidak dapat membuat instance dari sebuah interface. Contohnya: Interface maupun class dapat mendefinisikan method. Sebuah interface tidak punya sebuah kode implementasi sedangkan class memiliki salah satunya
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Membuat Interface Mari kita ambil contoh class Line dimana berisi method yang menghitung panjang dari garis dan method yang membandingkan object Line ke object dari class yang sama. Sekarang, misalkan kita punya class yang lain yaitu MyInteger dimana berisi method yang membandingkan object MyInteger ke object dari class yang sama.
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Membuat Interface Kedua class tersebut mempunyai method yang mirip yaitu membandingkan suatu object dari object lain dalam tipe yang sama, tetapi mereka tidak berhubungan sama sekali. Supaya dapat menjalankan cara untuk memastikan bahwa dua class tersebut mengimplementasikan beberapa method dengan tanda yang sama, kita dapat menggunakan sebuah interface. Misal : interface Relation yang mempunyai deklarasi method pembanding.
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Interface yang mendefinisikan hubungan antara dua object menurut urutan asli dari object.
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Penggunaan Interface Penggunaan interface, kita gunakan kata kunci implements. Contohnya,
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Note Ketika class Anda mencoba mengimplementasikan sebuah interface, selalu pastikan bahwa Anda mengimplementasikan semua method dari interface, jika tidak, Anda akan menemukan kesalahan
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Hubungan dari Interface ke Class Class dapat mengimplementasikan sebuah interface selama kode implementasi untuk semua method yang didefinisikan dalam interface tersedia Class hanya dapat meng-EXTEND SATU superclass, tetapi dapat meng-IMPLEMENTASIkan BANYAK interface
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Hubungan dari Interface ke Class class yang mengimplementasikan interface
class yang meng-extend satu superclass dan mengimplementasikan sebuah interface
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Note Sebuah interface bukan bagian dari hirarki pewarisan class. Class yang tidak berhubungan dapat mengimplementasikan interface yang sama
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Latihan Buat interface MakhlukHidup Makan Berjalan Bersuara
Buat interface Identitas TampilkanNama TampilkanUmur
Buat class Manusia dan Hewan Manusia mengimplementasikan interface MakhlukHidup dan Identitas Hewan hanya mengimplementasikan MakhlukHidup 28
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