在沒有默認方法特性時，當你往接口中添加新方法時，接口內部所有實現(xiàn)的類都要歷經(jīng)一些修改，這將導致上千行的代碼修改工作量。為了避免這點，Java8引入了默認對象方法，亦即，如果你想要往現(xiàn)存的接口中添加任何功能，你只需添加默認方法特性而不會影響接口實現(xiàn)形式。那么java 8 接口默認方法有哪些特性，跟yjbys小編一起來來看看吧!

讓我們看一些例子來更好的理解它。例如，我聲明了一個具有打開和讀取功能的接口“BookIterface”。接口的類需要實現(xiàn)打開和讀取方法。

package org.smarttechie;

/**

* The interface is intended to open and read. The implementors should implement the methods to open and read.

* @author Siva Prasad Rao Janapati

*

*/

public interface BookInterface {

/**

* The method opens the book

*/

public void openTheBook();

/**

* The method reads the book

*/

public void readTheBook();

}

現(xiàn)在，我們提供上面接口的實現(xiàn)代碼

package org.smarttechie;

/**

* The JavaBookImpl is the implementation of BookInterface

* @author Siva Prasad Rao Janapati

*

*/

public class JavaBookImpl implements BookInterface {

/**

* This opens the book

*/

@Override

public void openTheBook() {

System.out.println("The Java book is opened");

}

/**

* This reads the book

*/

@Override

public void readTheBook() {

System.out.println("Reading the Java book");

}

}

現(xiàn)在，我們想要給接口提供一個關閉功能。如果你直接添加關閉功能到book接口中，現(xiàn)存的實現(xiàn)類需要歷經(jīng)一些修改。有了默認方法特性后，我們能給book接口直接添加關閉功能。默認方法對所有實現(xiàn)都可用。

package org.smarttechie;

/**

* The interface is intended to open and read. The implementors should implement the methods to open and read.

* @author Siva Prasad Rao Janapati

*

*/

public interface BookInterface {

/**

* The method opens the book

*/

public void openTheBook();

/**

* The method reads the book

*/

public void readTheBook();

/**

* The default method implementation

*/

public default void closeTheBook() {

System.out.println("Closting the book");

}

}

package org.smarttechie;

/**

* The JavaBookImpl is the implementation of BookInterface

* @author Siva Prasad Rao Janapati

*

*/

public class JavaBookImpl implements BookInterface {

/**

* This opens the book

*/

@Override

public void openTheBook() {

System.out.println("The Java book is opened");

}

/**

* This reads the book

*/

@Override

public void readTheBook() {

System.out.println("Reading the Java book");

}

public static void main (String[] args) {

BookInterface bookInter = new JavaBookImpl();

//Call the default method declared in BookInterface

bookInter.closeTheBook();

JavaBookImpl book = new JavaBookImpl();

book.closeTheBook();

}

}

下面給出了上述調用方法的字節(jié)碼。從字節(jié)碼中，我們可以認為默認方法是一種“虛方法”。

如果你想，你可以重載實現(xiàn)類中的默認方法：

package org.smarttechie;

/**

* The JavaBookImpl is the implementation of BookInterface

* @author Siva Prasad Rao Janapati

*

*/

public class JavaBookImpl implements BookInterface {

/**

* This opens the book

*/

@Override

public void openTheBook() {

System.out.println("The Java book is opened");

}

/**

* This reads the book

*/

@Override

public void readTheBook() {

System.out.println("Reading the Java book");

}

/*

* This closes the book

*/

public void closeTheBook() {

System.out.println("Closing the JAVA book");

}

public static void main (String[] args) {

BookInterface book = new JavaBookImpl();

book.closeTheBook();

}

}

到這會兒，你可能有一個疑問，如果我們實現(xiàn)了兩個具有同樣默認方法簽名的接口會怎樣?在那種情況下，調用實現(xiàn)會得到下面的編譯錯誤提示。

“用參數(shù)()和()復制名為closedTheBook的默認方法是繼承于TheBookInterface和BookInterface的類型。”

package org.smarttechie;

public interface TechBookInterface {

/**

* The default method implementation

*/

public default void closeTheBook() {

System.out.println("Closing the book");

}

}

package org.smarttechie;

/**

* The JavaBookImpl is the implementation of BookInterface

* @author Siva Prasad Rao Janapati

*

*/

public class JavaBookImpl implements BookInterface, TechBookInterface {

/**

* This opens the book

*/

@Override

public void openTheBook() {

System.out.println("The Java book is opened");

}

/**

* This reads the book

*/

@Override

public void readTheBook() {

System.out.println("Reading the Java book");

}

public static void main (String[] args) {

BookInterface book = new JavaBookImpl();

book.closeTheBook();

}

}

為了避免這個編譯錯誤，我們需要在實現(xiàn)類中顯式地定義那個具有同樣簽名的方法。

package org.smarttechie;

/**

* The JavaBookImpl is the implementation of BookInterface

* @author Siva Prasad Rao Janapati

*

*/

public class JavaBookImpl implements BookInterface, TechBookInterface {

/**

* This opens the book

*/

@Override

public void openTheBook() {

System.out.println("The Java book is opened");

}

/**

* This reads the book

*/

@Override

public void readTheBook() {

System.out.println("Reading the Java book");

}

public void closeTheBook() {

System.out.println("Closing the JAVA book");

}

public static void main (String[] args) {

BookInterface book = new JavaBookImpl();

book.closeTheBook();

}

}

總結

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