equals

Please help me how does the string.equals in java work with null value? Is there some problem with exceptions? Three cases: boolean result1,result2, result3; //1st case String string1 = null; String string2 = null; result = string1.equals(string2); //2nd case String string1 = "something"; String string2 = null; result2 = string1.equals(string2); //3rd case String string1 = null; String string2 = "something"; result3 = string1.equals(string2); What the values of results are? I expect this values: result1 is true; result2 is false; result3 is false; You cannot use the dereference (dot, '.')

I'm reviewing a manual of best practices and recommendation coding java I think is doubtful. Recomendation: String variable; "xx".equals(variable) // OK variable.equals("xx") //Not recomended Because prevents appearance of NullPointerException that are not controlled Is this true? Mark Byers This is a very common technique that causes the test to return false if the variable is null instead of throwing a NullPointerException . But I guess I'll be different and say that I wouldn't regard this as a recommendation that you always should follow. I definitely think it is something that all Java

Im overriding an equals() method and I need to know if the object is an instance of a Event's subclass (Event is the superclass). I want something like "obj subclassof Event". How can this be made? Thanks in advance! instanceof can handle that just fine. Adrian With the following code you can check if an object is a class that extends Event but isn't an Event class instance itself. if(myObject instanceof Event && myObject.getClass() != Event.class) { // then I'm an instance of a subclass of Event, but not Event itself } By default instanceof checks if an object is of the class specified or a

It (should, to me,) say True if there are only vowels in the string(phrase); otherwise says False . I don't understand why it always will return False , since (x >= x) always returns True . I thank anyone for checking the solution to this query. (str) -> bool def valid_letter_sequence(abc): valid_letters = abc.count('A') + abc.count('E') + abc.count('I') + abc.count('O') + abc.count('U') counted_letters = abc.count('') if valid_letters >= counted_letters: return True else: return False Observe: >>> 'abc'.count('') 4 Passing an empty string to count gives you one more than the length of the

I have the classes below: public class Sample implements java.io.Serializable{ //POJO with two fields and getters/setters private String name; private Integer id; //This POJO does not override equals() and hashCode() } public class B{ private Sample sample; //here i need override hashcode and equals() based on **sample** property. } When i tried overriding equals() and hashCode() in the B class I got the error below in Eclipse. The field type com.mypackage.Sample does not implement hashCode() and equals() - The resulting code may not work correctly. Now how can I compare two B instances

I want to see if a character in my string equals a certain other char value but I do not know what the char in the string is so I have used this: if ( fieldNames.charAt(4) == "f" ) But I get the error: "Operator '==' cannot be applied to 'char', 'jav.lang.String'" But "g" == "h" seems to work and I know you can use '==' with char types. Is there another way to do this correctly? Thanks! Madhawa Priyashantha if ( fieldNames.charAt(4) == 'f' ) because "f" is a String and fieldNames.charAt(4) is a char . you should use 'f' for check char "g" == "h" works because both g and h are Strings and you