Java with null

A null value indicates the absence of a column value in a row. A null value is an unknown value; it is not the same as zero or all blanks. And, if we tried to invoke any methods on nullValue, we'd get a NullPointerException, as expected. To check if it is null, we call the isNull method and pass the object getUserObject as a parameter. It returns true as the passed object is null. Absolutely not. An empty string and a null string are entirely different things and you should not confuse them.

To explain further: "null" means "I haven't initialized this variable, or it has no value". In Java, a null value can be assigned to an object reference of any type to indicate that it points to nothing. The compiler assigns null to any uninitialized static and instance members of reference type.

Hubert Kario Jim Jeffries Jim Jeffries 9, 13 13 gold badges 58 58 silver badges bronze badges. The easiest thing is to try null checking with equals and see. When you try it will instantly be obvious — Goran Jovic. By the way, a google search with keywords "java null check" without quotes gave me as one of the top hits this thread , which has the same info as the answers here.

Add a comment. Active Oldest Votes. Crowder T. Crowder k gold badges silver badges bronze badges. Xepoch: No, I don't generally create public fields although it doesn't really matter for this example either way.

Crowder "They're two completely different things.. However, the default implementation of both is the same, if my understanding is correct. Looking at the source code,. Ayush - That's the default in Object , yes.

It's overridden by a large number of the JDK classes, though. But the point about isn't about implementation, it's about semantics. Side note: JDK7 is very out of date. RogerWang - Good question! The answer is that null isn't an object, it's an object reference a blank one. It's the only object reference we can write literally in code.

Show 2 more comments. Community Bot 1 1 1 silver badge. Your example is generally better written as if "hi". If your object reference is null, then the call someObject. ColinD Agree just demonstrating here — jmj. It's always advisable to avoid nulls at all cost, so you don't need null checks at all ;. Learn more. Best way to handle nulls in Java? Asked 10 years, 10 months ago. Active 3 years, 7 months ago. Viewed 92k times. Improve this question.

Chris 5, 3 3 gold badges 26 26 silver badges 39 39 bronze badges. Shaun F Shaun F 1 1 gold badge 2 2 silver badges 6 6 bronze badges. Why would you not "fix the cause of the null"? Can you provide an example of why this isn't the only sensible choice?

Clearly, something must be pushing you away from the obvious. What is it? Why isn't fix the root cause your first choice?

Well fixing the "root cause" of the issue may help in the short term, but if the code is still not defensively checking for nulls and is reused by another process that may introduce a null, i would have to fix it again. Shaun F: If the code is broken, it's broken. I don't get how it's possible for code to produce unexpected nulls and not get fixed. Clearly, there's some "dumb management" or "political" stuff going on. Or something that allows erroneous code to be somehow acceptable.

Can you explain how erroneous code is not getting fixed? What's the political background that leads you to ask this question? If "I can fix the data creation routine" then there is no further vulnerability. I'm unable to understand what this "later data creation that had nulls in it" can possibly mean? Buggy software? Lott, encapsulation and single responsibility. All your code doesn't "know" what all your other code does. If a class accepts Froobinators, it makes as few assumptions as possible about who created the Froobinator and how.

It make come from "external" code, or it make just come from a different part of the code base. I'm not saying you shouldn't fix buggy code; but search "defensive programming" and you'll find what the OP is referring to.

Show 3 more comments. Active Oldest Votes. Improve this answer. It's really as simple as that. Guava has some very nice helper methods making the null check as simple as Precondition.

See stackoverflow. My rule is to initialize everything to sensible defaults if possible and worry about null exceptions afterwards. In some cases, doing the early check might be useful or even necessary; but I fear lots of senseless boilerplate null checks that add little value and just make the program larger.

If null is not a reasonable input parameter to your method but calls of the method are likely to accidentally pass null especially if the method is public , you may also want to have your method throw an IllegalArgumentException when given null.

This signals to callers of the method that the bug is in their code rather than in the method itself. Show 1 more comment. Don't use null, use Optional As you've pointed out, one of the biggest problems with null in Java is that it can be used everywhere , or at least for all reference types. It's impossible to tell that could be null and what couldn't be. Java 8 introduces a much better pattern: Optional. On the other hand, if null could be used and mean something, make sure to use it.

Quazi Irfan 6 6 bronze badges. Paul Draper Paul Draper 5, 3 3 gold badges 21 21 silver badges 36 36 bronze badges. Normally, answers to four year old questions end up deleted due to low quality. About This Article. Co-authored by:. Co-authors: Updated: June 3, Categories: Java. Italiano: Utilizzare l'Istruzione Null in Java.

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