is it possible for a class in java to have no constucror...

Vikash Verma · 2012-06-18T23:54:15+00:00

I am finding no constructor while using javap tool for my java class...

is it possible for a class in java to have no constucror...

Vikash Verma

Member

Updated: Oct 26, 2024

Views: 1.1K

I am finding no constructor while using javap tool for my java class...

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Anoop Kumar

Member • Jun 19, 2012

Didn't used javap command..
but default constructor always added to class file, either it written in source code or not. did you tried for it JD java decompiler to generate source file from class file.

If you have any doubt just call super(); as first line in subclass *constructor without having any constructor in super class. see what will happen!!!!😀

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Neeraj Sharma

Member • Jun 19, 2012

No need at all. There is always a default constructor as follows even if you dont declare yours,
It has following structure.
public class_name
{
}

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sookie

Member • Jun 19, 2012

#-Link-Snipped-# I am getting the default constructor getting displayed for my java class using javap. Can you please share your java class along with javap command results?

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Vikash Verma

Member • Jun 19, 2012

getting following error while using super(); in subclass constructor...😎

C:\Users\VIK\Desktop>javac *.java
B.java:6: cannot find symbol
symbol : constructor A()
location: class A
super();
^
1 error

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Vikash Verma

Member • Jun 19, 2012

I am getting no constructor using javap tool in my, class here goes the output of my class... 😎

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Anoop Kumar

Member • Jun 19, 2012

your code please...

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Vikash Verma

Member • Jun 19, 2012

#-Link-Snipped-# does it always happen that for each and every java program javap tool will display at least one constructor...😎

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Anoop Kumar

Member • Jun 20, 2012

Vikash Verma
#-Link-Snipped-# does it always happen that for each and every java program javap tool will display at least one constructor...😎

Sure it will show you all class members using command javap -private <ClassName>
If your code is like this one

class super1{
}
public class HelloWorld extends super1{
    HelloWorld (String s)    {
          s="ABC"    ;
        }
public static void main(String[] args) {
        System.out.println("Hello, World");
    }
}

Then compile the code and use javap you will get following output

C:\Documents and Settings\<User>\My Documents\Downloads>javap -private Hell
oWorld
Compiled from "HelloWorld.java"
public class HelloWorld extends super1{
    HelloWorld(java.lang.String);
    public static void main(java.lang.String[]);
}

For class super1.

C:\Documents and Settings\<user>\My Documents\Downloads>javap -private supe
r1
Compiled from "HelloWorld.java"
class super1 extends java.lang.Object{
    super1();
}

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Vikash Verma

Member • Jun 21, 2012

This is what my code is displaying...😎

C:\Users\VIK\Desktop>javac B.java

C:\Users\VIK\Desktop>javap B
Compiled from "B.java"
class B extends java.lang.Object{
public static void main(java.lang.String[]);
}

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sookie

Member • Jun 21, 2012

Vikash Verma
This is what my code is displaying...😎

C:\Users\VIK\Desktop>javac B.java

C:\Users\VIK\Desktop>javap B
Compiled from "B.java"
class B extends java.lang.Object{
public static void main(java.lang.String[]);
}
And can you Please tell what is your code? B.java?

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sookie

Member • Jun 21, 2012

I was just trying something and came to know that may be your B.java has declared constructor as "private" If you have its visibility as "private" then following command "javap B" will not show the private constructor. In order to view it you will have t explicitly run the command as "javap -private B".

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Anoop Kumar

Member • Jun 21, 2012

my JDK giving error while running javap B.
While "javap -private B". is working fine.
#-Link-Snipped-# , can you confirm this.

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sookie

Member • Jun 21, 2012

ianoop
my JDK giving error while running javap B.
While "javap -private B". is working fine.
#-Link-Snipped-# , can you confirm this.
show me the error and your B.java ?

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Anoop Kumar

Member • Jun 21, 2012

sookie
show me the error and your B.java ?

😲, its working, what's wrong , I was doing

Here is final conclusion

 
 
With public constructor
Source:
public class abc{
   
    abc(){}   
    public static void main(String[] args) {
        System.out.println("Hello, World");
    }
 
}
Output
 
C:\Documents and Settings\<user>\My Documents\Downloads>javap  abc
Compiled from "abc.java"
public class abc extends java.lang.Object{
    public abc();
    public static void main(java.lang.String[]);
}
 
With private constructor
Source:
public class abc{
   
    private abc(){}   
    public static void main(String[] args) {
        System.out.println("Hello, World");
    }
 
}
Output
 
C:\Documents and Settings\<user>\My Documents\Downloads>javap  abc
Compiled from "abc.java"
public class abc extends java.lang.Object{
    public static void main(java.lang.String[]);
}
 
With private constructor
C:\Documents and Settings\<user>\My Documents\Downloads>javap -private abc
Compiled from "abc.java"
public class abc extends java.lang.Object{
    private abc();
    public static void main(java.lang.String[]);
}

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sookie

Member • Jun 21, 2012

ianoop
😲, its working, what's wrong , I was doing
Cool...😀

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Vikash Verma

Member • Jun 24, 2012

#-Link-Snipped-# you are right...😎

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