Why we can't extends more than one class

Question

well, I am currently developing an application which uses JFrame and Applet.

Why we can't extend both..

public class myClass extends Applet, javax.swing.JFrame {...}
//invalid...

The valid code is.

public class myClass extends Applet {
    javax.swing.JFrame frame = new javax.swing.JFrame();
    public void init(){
        frame.setSize(300, 400);
        frame.setVisible(true);
    }
}

Why so? Why we can't extends more than one class

This question appears to be off-topic because it cannot be answered definitively. Java simply does not support multiple inheritance. — Jeroen Vannevel, Apr 04 '14 at 13:31
I usually make my main application component a subclass of JPanel. You can then embedded that component as the main component in a JApplet or a JFrame. With minimal extra code you can than have your application work as a Swing desktop app or an applet. — Paul, Apr 04 '14 at 13:53

Reimeus · Accepted Answer · 2014-04-04T21:01:16.333

9

The designers of Java learned from the mistakes made in other languages such as C++ where the diamond problem was an issue caused by multiple inheritance so decided to make Java a single inheritance language to simplify development.

edited Apr 04 '14 at 21:01

answered Apr 04 '14 at 13:31

Reimeus

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score 0 · Answer 2 · answered Apr 04 '14 at 13:30

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This is how Java works. It just doesn't support multiply inheritance. There are many reasons why multiply inheritance may be dangerous. For example there can be a name conflict.

On the other hand you can implement as many interfaces as you want to.

answered Apr 04 '14 at 13:30

Jakub H

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score 0 · Answer 3 · answered Apr 04 '14 at 13:32

When a class is abstract or extended, you are specifying the role that the class plays. This also helps to prevent looping inheritence.

An interface is merely a contract that you will have provided method functionality in your class. If you want to inherit from multiple sources that don't specify the role of the class, use an interface.

score 0 · Answer 4 · answered Apr 04 '14 at 13:33

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Just like what Jakub said, multiple inheritance is not supported in java so you will have to use interfaces instead. It's just the nature of the language. I do hope that's what you're asking.

answered Apr 04 '14 at 13:33

ron weasly

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score 0 · Answer 5 · edited May 23 '17 at 11:44

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Java does not allowed multiple inheritance nativelly but you can simulate the "multi-inheritance" like that see.

Or you can use Java8 which allow you to use specific interface in which you can implement ONE method.

edited May 23 '17 at 11:44

Community

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answered Apr 04 '14 at 13:34

Kraiss

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score 0 · Answer 6 · answered Apr 04 '14 at 13:35

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Multiple inheritance is not supported in java, to get around this the concept of Interfaces is used. You can inherit from as many interfaces you like to achieve multiple inheritance.

answered Apr 04 '14 at 13:35

Harry

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Why we can't extends more than one class

6 Answers6