Java instanceof doesn't work in my case

Question

I have the following classes inheritance structure:

public class Document {}
public class AuditProgramDocument extends Document {}
public class CaseFilePart {
    private Document document;
    public Document getDocument() {
        return document;
    }
}
public class MyClass {
    public boolean canDeleteDocument(CaseFilePart selectedCFP) {
        ...//somelogic
        if (selectedCFP.getDocument() instanceof AuditProgramDocument) {
            System.out.println("instance");
        }
    }
}

In debugger, I clearly see that, selectedCFP.getDocument() returns AuditProgramDocument. But If statement doesn't evaluated.

My test:

System.out.println("2.1 " + selectedCFP.getDocument().getClassName());
System.out.println("2.2 " + selectedCFP.getDocument().getClass().getName());
System.out.println("2.3 " + selectedCFP.getDocument().getClass().getCanonicalName());
System.out.println("2.4 " + selectedCFP.getDocument().getClass().getSimpleName());

Results in output:
2.1 auditProgramDocument
2.2 eu.erp.crams.cmg.bom.document.Document$$_javassist_79_
2.3 eu.erp.crams.cmg.bom.document.Document$$_javassist_79_
2.4 Document$$_javassist_79_

Try to print selectedCFP.getDocument() before the if. In general: stuff works; if things are broken, then in 99.999999% of time, it is your code. — GhostCat
– GhostCat, Commented Jun 13, 2016 at 12:09
@Beezy Is 2.1 actually auditProgramDocument (lowercase a), or is it AuditProgramDocument (uppercase A)? — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Jun 13, 2016 at 12:21
It IS a different class... 2.2 eu.erp.crams.cmg.bom.document.Document$$_javassist_79_ — Niels
– Niels, Commented Jun 13, 2016 at 12:28
The output of getClassName() means almost nothing. It’s not a standard Java method, it’s a method you wrote. Perhaps you should include the code for that method in your question. The code for the toString method of Document and its subclasses might also be useful. — VGR
– VGR, Commented Jun 13, 2016 at 14:22

BSeitkazin · Accepted Answer · 2016-06-14 04:50:32Z

3

So, to be sure we have the following rules:

AuditProgramDocument is Document

CaseFilePart has Document

When we write the code:

Document document = new AuditProgramDocument();
if (document instanceof Document) //true
if (document instanceof AuditProgramDocument) //true

But, when we write the code:

Document document = someVar.getDocument();
if (document instanceof Document) //true
if (document instanceof AuditProgramDocuemtn) //false

The last statement is false because Document is not AuditProgramDocument. Because the getDocument() method always returns us reference to Document, not subtype

answered Jun 14, 2016 at 4:50

BSeitkazin

3,10927 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Brijmohan Pant · Accepted Answer · 2016-06-13 12:48:14Z

0

1)-:In side CaseFilePart class you are creating reference variable of Document class not object of document class.

You should return object of Document class not reference.

2)-:AuditProgramDocument class is child class of Document class we can not down cast it.

3)-:that is why selectedCFP.getDocument() not instanceof AuditProgramDocument

answered Jun 13, 2016 at 12:48

Brijmohan Pant

92 bronze badges

Comments

Bradley D · Accepted Answer · 2016-06-14 13:27:59Z

Try this code... (commented out, but included your original tests)

public class MyClass {
    public boolean canDeleteDocument(Document doc) {
        return (doc instanceof AuditProgramDocument);
    }

    public static void main(String[] args) {
        //System.out.println("2.1 " + selectedCFP.getDocument().getClassName());//DOES NOT COMPILE
        //Not sure about these tests....
        //System.out.println("2.2 " + selectedCFP.getDocument().getClass().getName());
        //System.out.println("2.3 " + selectedCFP.getDocument().getClass().getCanonicalName());
        //System.out.println("2.4 " + selectedCFP.getDocument().getClass().getSimpleName());

        MyClass mc = new MyClass();
        CaseFilePart cfp = new CaseFilePart();

        //TEST 1
        cfp.setDocument(new AuditProgramDocument());
        boolean canDelete = mc.canDeleteDocument(cfp.getDocument());
        System.out.println("Can we delete " + cfp.getDocument().getClass() + " " + canDelete);

        //TEST 2
        cfp.setDocument(new SomeOtherDocument());
        canDelete = mc.canDeleteDocument(cfp.getDocument());
        System.out.println("Can we delete " + cfp.getDocument().getClass() + " " + canDelete);
    }

}

//Put all these in the same file to simplify the answer
class Document {}
class AuditProgramDocument extends Document {}
//Created 2nd Document implementation for illustration
class SomeOtherDocument extends Document {}
class CaseFilePart {
    private Document document;
    public Document getDocument() {
        return document;
    }

    public void setDocument(Document document) {
        this.document = document;
    }
}

Collectives™ on Stack Overflow

Java instanceof doesn't work in my case

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related