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I want to build upon org.apache.commons.lang3.StringUtils and add a certain method specific for a problem of mine. So I try to inherit from the commons class and write

package org.test.project;

public class StringUtils extends org.apache.commons.lang3.StringUtils {

    public static boolean myMethod(final String cs) {
        // My method body
    }

}

Now, I want to use the method public static boolean isEmpty(final CharSequence cs) from org.apache.commons.lang3.StringUtils in another part of my code. As I recall and from this thread a String is a CharSequence. Thus, I write

package org.test.project.package;

import org.test.project.StringUtils;

public class TestClass{

    public void someMethod(String s){

        if (StringUtils.isEmpty(s)){
            // do stuff
        }
    }
}

Why do I get the error:

cannot find symbol
symbol: method isEmpty(String)
location: class StringUtils

in my IDE?

From here I have the info that "All methods that are accessible are inherited by subclasses." Therein, it is also stated

The only difference with inherited static (class) methods and inherited non-static (instance) methods is that when you write a new static method with the same signature, the old static method is just hidden, not overridden.

But I do not have a method isEmpty with the same erasure.

Edit

So, thanks to @luksch, I added a method

public static boolean isEmpty(final String cs) {
    return isEmpty((CharSequence)cs);
}

in my StringUtils class and that works. However, for testing I want to call public static String center(final String str, final int size) from the commons library. So I write

package org.test.project.package;

import org.test.project.StringUtils;

public class TestClass{

    public void someMethod(String s){

        if (StringUtils.isEmpty(s)){
            // do stuff
        }

        String test = StringUtils.center("test",10);

    }
}

I do not have any kind of method center my StringUtils subclass. So I thought, it would just automatically call the method from org.apache.commons.lang3.StringUtils. However, I get the equivalent error message as above:

cannot find symbol
symbol: method center(String,int)
location: class StringUtils

Why?

raedma
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    does it work when you cast to ```CharSequence``` in your call of ```isEmpty``` inside ```someMethod```? – luksch Jun 09 '19 at 16:04
  • Thanks, that seems to work. – raedma Jun 10 '19 at 09:20
  • You don't need to `extend` from StringUtils. In fact, that will probably end up confusing things. The preferred method is to call the static methods directly (you can use static imports if you need them a lot). – Thilo Jun 10 '19 at 10:15
  • (but what you are doing should work... ) – Thilo Jun 10 '19 at 10:18
  • Thanks, I know that I don't have to extend from commons-lang `StringUtils`. However, I do have classes that use method from my `StringUtils` and commons-lang `StringUtils` extensively, and I do not always want to write the full class name for the sake of clearness. That is where my question arises from. – raedma Jun 10 '19 at 10:19
  • Ok, everything works. It was just a matter of updating a dependency in my code as my `StringUtils` is in another project. – raedma Jun 10 '19 at 10:20

0 Answers0