How can I use object inside if statement I tried 2 ways one like this:   import java.util.Scanner;  public class Species{  String kind;  public void talk() { System.out.println(kind + " is talking");} public void walk() { System.out.println(kind + " is walking");} public void swim() { System.out.println(kind + " is swimming");} public void check() {       if (kind == "woman") {talk(); walk();}     else if (kind == "fish") {swim();}     else System.out.println("Sorry not one of our option."); }  public static void main(String [] args) {      Scanner read = new Scanner (System.in);      Species sp1 = new Species();      sp1.kind = null ;      System.out.print("Enter a kind: ");     sp1.kind = read.nextLine();      sp1.check();  }}    And another one:  import java.util.Scanner;  public class Species{  String kind;  public void talk() { System.out.println(kind + " is talking");} public void walk() { System.out.println(kind + " is walking");} public void swim() { System.out.println(kind + " is swimming");}   public static void main(String [] args) {      Scanner read = new Scanner (System.in);      Species sp1 = new Species();      sp1.kind = null ;      System.out.print("Enter a kind: ");     sp1.kind = read.nextLine();      if (sp1.kind == "woman") {sp1.talk(); sp1.walk();}     else if (sp1.kind == "fish") {sp1.swim();}     else System.out.println("Sorry not one of our option.");           }}   Each time it shows the message Sorry not one of our option I know it's a simple program but it wouldn't work
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I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?
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Okay, we know that the following two lines are equivalent -    (0 == i) (i == 0)   Also, the first method was encouraged in the past because that would have allowed the compiler to give an error message if you accidentally used '=' instead of '=='.  My question is - in today's generation of pretty slick IDE's and intelligent compilers, do you still recommend the first method?    In particular, this question popped into my mind when I saw the following code -   if(DialogResult.OK == MessageBox.Show("Message")) ...    In my opinion, I would never recommend the above. Any second opinions?
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I'm implementing compareTo() method for a simple class such as this (to be able to use Collections.sort() and other goodies offered by the Java platform):  public class Metadata implements Comparable&lt;Metadata&gt; {     private String name;     private String value;  // Imagine basic constructor and accessors here // Irrelevant parts omitted }   I want the natural ordering for these objects to be: 1) sorted by name and 2) sorted by value if name is the same; both comparisons should be case-insensitive. For both fields null values are perfectly acceptable, so compareTo must not break in these cases.   The solution that springs to mind is along the lines of the following (I'm using "guard clauses" here while others might prefer a single return point, but that's beside the point):  // primarily by name, secondarily by value; null-safe; case-insensitive public int compareTo(Metadata other) {     if (this.name == null &amp;&amp; other.name != null){         return -1;     }     else if (this.name != null &amp;&amp; other.name == null){         return 1;     }     else if (this.name != null &amp;&amp; other.name != null) {         int result = this.name.compareToIgnoreCase(other.name);         if (result != 0){             return result;         }     }      if (this.value == null) {         return other.value == null ? 0 : -1;     }     if (other.value == null){         return 1;     }      return this.value.compareToIgnoreCase(other.value); }   This does the job, but I'm not perfectly happy with this code. Admittedly it isn't very complex, but is quite verbose and tedious.  The question is, how would you make this less verbose (while retaining the functionality)? Feel free to refer to Java standard libraries or Apache Commons if they help. Would the only option to make this (a little) simpler be to implement my own "NullSafeStringComparator", and apply it for comparing both fields?  Edits 1-3: Eddie's right; fixed the "both names are null" case above  About the accepted answer  I asked this question back in 2009, on Java 1.6 of course, and at the time  was my preferred accepted answer. I never got round to changing that until now (2017).  There are also —a 2009 Apache Commons Collections one and a 2013 Guava one, both posted by me—that I did prefer at some point in time.  I now made the clean  the accepted answer. That should definitely be preferred if on Java 8, and these days Java 8 should be available to nearly all projects.
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I have a lookup to a custom object called Project on my Opportunity object. I am trying to write a trigger that updates an Active, Awarded, and Title on the Project object whenever the Active, Awarded, or Title field is updated on Opportunity based some on more logic that isn't in my code below. This is my first trigger and needing a little help due to a NullPointerException where I try to set Project__r.Active__c = true. Any thoughts?      trigger ProjectFieldsTrigger on Opportunity (before insert, before update) {       //List&lt;Opportunity&gt; opp = [SELECT Name, Active__c, Funded__c, Title__c, Project__r.Name, Project__r.Active__c, Project__r.Awarded__c      //  FROM Opportunity WHERE Id IN :Trigger.New];      for(Opportunity o: Trigger.New){          if(o.Project__c != null){              if(o.Active__c == 'Y'){                 o.Project__r.Active__c = true;             }      }  }
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I would like to print the "object reference" of an object in Java for debugging purposes. I.e. to make sure that the object is the same (or different) depending on the situation.  The problem is that the class in question inherits from another class, which has overriden both toString() and hashCode() which would usually give me the id.  Example situation: Running a multi-threaded application, where I (during development) want to check if all the threads use the same instance of a resource object or not.
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what about using "this" with methods in Java? Is it optional or there are situations when one needs to use it obligatory?  The only situation I have encountered is when in the class you invoke a method within a method. But it is optional. Here is a silly example just to show what I mean:  public class Test {      String s;      private String hey() {         return s;     }      public String getS(){         String sm = this.hey();         // here I could just write hey(); without this         return sm;     } }
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Which is the right thing to do?  if (myObj['key'] == undefined)   or  if (myObj['key'] == null)   or  if (myObj['key'])
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This is a canonical question and answer developed by the community to help address common questions. If you've been directed here, or your question has been closed as a duplicate, please look through the resources here and use them to shape more specific questions. To browse all canonical questions and answers, navigate to the  tag. This question and answer is owned by the community! If you can improve it and make it more useful, you're welcome to edit it. I am building a trigger, a unit test, or other Apex code. I'm working with sObject records, and trying to access related record information. For example, I might have a structure like this: Account a = new Account(Name = 'Test'); insert a;  Opportunity o = new Opportunity(Name = 'Donation', AccountId = a.Id); insert o;  System.assertEquals(o.Account.Name, 'Test', 'Correct Account associated'); // Assertion fails!  Or, in a trigger, I might be aiming for something like this: trigger ContactTrigger on Contact (after insert) {     for (Contact c : Trigger.new) {         if (c.Account.Name == 'Test') {             // Take some action here         }      } }  Why doesn't this work? Why am I getting null values, or NullPointerExceptions?
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if ('text'.equals(str))   or   if ('text' == str)   Is there any difference? If yes, then what is it?   Added, after answered.  String q = 'teXt'; system.debug('teXt'.equals(q)); // true system.debug('teXt' == q);      // true system.debug('text'.equals(q)); // false system.debug('text' == q);      // true
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Please demonstrate how the ternary operator works with a regular if/else block. Example:  Boolean isValueBig = value &gt; 100 ? true : false;     Exact Duplicate:
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I came across this code and wanted others to provide their point of view... is it good or bad ? ;)  Class ReportClass {  public string ReportName {get; set;} }   Then it was used as follows in code:  displayReport(ReportClass.ReportName = cmbReportName.SelectedValue.ToString())   That is about the simplest form example I can give you. Quetion is... why can't I find examples ? What would this be called? Is this just asking for trouble?  EDIT: I'm referring to the inplace assignment. Which I wasn't aware of until today
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I'm wanting to parse a string into a nullable int in C#.  ie. I want to get back either the int value of the string or null if it can't be parsed.  I was kind of hoping that this would work  int? val = stringVal as int?;   But that won't work, so the way I'm doing it now is I've written this extension method  public static int? ParseNullableInt(this string value) {     if (value == null || value.Trim() == string.Empty)     {         return null;     }     else     {         try         {             return int.Parse(value);         }         catch         {             return null;         }     } }      Is there a better way of doing this?  EDIT:  Thanks for the TryParse suggestions, I did know about that, but it worked out about the same.  I'm more interested in knowing if there is a built-in framework method that will parse directly into a nullable int?
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Here's the scenario...    if (entry.Properties["something"].Value != null)   attribs.something = entry.Properties["something"].Value.ToString();   While effective and working correctly, this looks ugly to me.  If I don't check for a null before performing the ToString() then it throws an exception if the property was null.  Is there a better way to handle this scenario?  Much appreciated!
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I ran into an interesting (and very frustrating) issue with the equals() method today which caused what I thought to be a well tested class to crash and cause a bug that took me a very long time to track down.   Just for completeness, I wasn't using an IDE or debugger - just good old fashioned text editor and System.out's. Time was very limited and it was a school project.  Anyhow -   I was developing a basic shopping cart which could contain an ArrayList of Book objects. In order to implement the addBook(), removeBook(), and hasBook() methods of the Cart, I wanted to check if the Book already existed in the Cart. So off I go -  public boolean equals(Book b) {     ... // More code here - null checks     if (b.getID() == this.getID()) return true;     else return false; }   All works fine in testing. I create 6 objects and fill them with data. Do many adds, removes, has() operations on the Cart and everything works fine. I read that you can either have equals(TYPE var) or equals(Object o) { (CAST) var } but assumed that since it was working, it didn't matter too much.  Then I ran into a problem - I needed to create a Book object with only the ID in it from within the Book class. No other data would be entered into it. Basically the following:  public boolean hasBook(int i) {     Book b = new Book(i);     return hasBook(b); }  public boolean hasBook(Book b) {     // .. more code here     return this.books.contains(b); }   All of a sudden, the equals(Book b) method no longer works. This took a VERY long time to track down without a good debugger and assuming the Cart class was properly tested and correct. After swaapping the equals() method to the following:  public boolean equals(Object o) {     Book b = (Book) o;     ... // The rest goes here    }   Everything began to work again. Is there a reason the method decided not to take the Book parameter even though it clearly  was  a Book object? The only difference seemed to be it was instantiated from within the same class, and only filled with one data member. I'm very very confused. Please, shed some light?
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It is much more convenient and cleaner to use a single statement like  import java.awt.*;   than to import a bunch of individual classes  import java.awt.Panel; import java.awt.Graphics; import java.awt.Canvas; ...   What is wrong with using a wildcard in the import statement?
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I am using java language,I have a method that is supposed to return an object if it is found. If it is not found, should I:  return null throw an exception other  Which is the best practise or idiom?
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Consider the following code:  void Handler(object o, EventArgs e) {    // I swear o is a string    string s = (string)o; // 1    //-OR-    string s = o as string; // 2    // -OR-    string s = o.ToString(); // 3 }   What is the difference between the three types of casting (okay, the 3rd one is not a casting, but you get the intent). Which one should be preferred?