What is the 'instanceof' operator used for in Java?

0 votes

What is the instanceof operator used for? I've seen stuff like

if (source instanceof Button) {
    //...
} else {
    //...
}

But none of it made sense to me. I've done my research, but came up only with examples without any explanations.

May 23, 2018 in Java by parth295
• 4,600 points
50 views

1 answer to this question.

0 votes

It's an operator that returns true if the left side of the expression is an instance of the class name on the right side.

Think about it this way. Say all the houses on your block were built from the same blueprints. Ten houses (objects), one set of blueprints (class definition).

instanceof is a useful tool when you've got a collection of objects and you're not sure what they are. Let's say you've got a collection of controls on a form. You want to read the checked state of whatever checkboxes are there, but you can't ask a plain old object for its checked state. Instead, you'd see if each object is a checkbox, and if it is, cast it to a checkbox and check its properties.

if (obj instanceof Checkbox)
{
    Checkbox cb = (Checkbox)obj;
    boolean state = cb.getState();
}
answered May 23, 2018 by Rishabh
• 3,540 points

Related Questions In Java

+1 vote
3 answers

What is the syntax to declare and initialize an array in java?

You can use this method: String[] strs = ...READ MORE

answered Jul 25, 2018 in Java by samarth295
• 2,190 points
203 views
0 votes
1 answer

What is the difference between Set and List in java?

List is an ordered sequence of elements. ...READ MORE

answered Apr 26, 2018 in Java by Akrati
• 3,150 points
66 views
0 votes
1 answer

What is the use of @Override annotation in Java ? When do we use it ?

I think it is most useful as ...READ MORE

answered May 4, 2018 in Java by Akrati
• 3,150 points
70 views
0 votes
1 answer

What is the difference == and equals() in Java?

Both the answers (Syntaxes) are correct. If ...READ MORE

answered Jun 5, 2018 in Java by Akrati
• 3,150 points
27 views
0 votes
1 answer

How do I replace character from string at specific indexes?

String are immutable in Java. You can't ...READ MORE

answered Apr 26, 2018 in Java by Rishabh
• 3,540 points
31 views
0 votes
1 answer

String mapping without Case-Sensitivity

Yes, contains is case sensitive. You can ...READ MORE

answered Feb 5 in Java by developer_1
• 3,280 points
25 views
0 votes
3 answers

Check if a String is numeric in Java

Java 8 Lambda Expression is used: String someString ...READ MORE

answered Sep 3, 2018 in Java by Daisy
• 8,040 points
563 views
0 votes
2 answers

“Could not find or load main class” mean?

Use the final modifier to enforce good initialization. Avoid returning ...READ MORE

answered Sep 18, 2018 in Java by Sushmita
• 6,840 points
1,392 views
0 votes
1 answer

What is the concept of Immutability for strings in Java ? Why are strings immutable ?

According to Effective Java, chapter 4, page 73, ...READ MORE

answered May 11, 2018 in Java by Rishabh
• 3,540 points
126 views
0 votes
2 answers

What is the use of toString method in Java and how can I use it ?

Whenever you require to explore the constructor ...READ MORE

answered Aug 23, 2018 in Java by Daisy
• 8,040 points
309 views