Thread: Compare method

Hello, I am writing a code that its showing the process of renewing your mail address when you move.

this is part of the program that i need help on

public class NewDataEntry 
	{
		private String name;
		private String oldAddress;
		private String newAddress;
 
 
 
		// a method that compares the old and the new address. if the address is the same the program     goes through it
		// if they are not the same it's false, and it needs the new address.
 
 
		// a subclass for a new entry if the addresses are not the same.
 
		public String getName()
		{
			return name;
		}
		public String getoldAddress()
		{
 
		}
		public String getnewAddress()
		{
 
		}
 
	}

i need a method that it will compare the oldAddress with the newAddress, when it is inputed.
if the new address that is inputed its the same thing as we have on file than the program skips that method but if its not, it has to compare and replace it with the new one....Im having hard time getting this ...can someone guide me?

Ok, this is a problem that I see ALL THE TIME with beginners to JAVA, so lets get this straight before it becomes an issue later down the line.

In JAVA, simple type numbers are compared for equality by using the double-equals (==) operation. Simple type numbers are ints, doubles, longs, floats, ect.

Objects are different however, and since String is essentially an Object, it follows the same comparing rules as all other Objects. Objects can be compared in two different ways, but each way does drastically different things. For Objects, if you are trying to check the values of the those Objects (like if two Strings are equal to each other) for equality, you cannot use the double-equals (==) operation. Instead, you have to use the XObject.equals(XObject) method, where XObject is a Comparable Object. Don't worry about Comparable Objects right now, just know that String is a Comparable Object. The second way to compare Objects is with the double-equals (==), however this doesn't check the value of the object. Instead, it checks the Object's value in memory. This is only necessary if you want to test if an Object has two or more variable names for whatever reason. From what I've found, fairly useless.

Now, String is unique in that it provides us with an additional way to compare. As well as the String.equals(String) method, there is also the String.equalsIgnoreCase(String) method. The difference is exactly what the method says. The first checks for equality, but is case sensitive. The second checks for equality, but ignores the case while doing so. Ignoring the case is useful if you want to compare two Strings together, but are unsure if they have the same case, but want them to equal each other regardless of what is capitalized and what isn't.

I usually ignore case when comparing Strings, simply because I take in a lot of user input and, as a programmer, you have to assume the user is an idiot and will incorrectly use your program or incorrectly input. As a result, you have to compensate for your user's stupidity ("ignorance", to be nice) and put in as many barriers and quick-fixes as possible to prevent the dreaded program crashes.

However, for your assignment, I'm not sure if you should be checking case or not while comparing Strings. That would be something to ask.

See Common Java Mistakes: == operator or equals() method

Originally Posted by Darryl.Burke

Sorry Aussie, but I feel a need to nitpick here to set the record straight.


1) They're called primitives. That includes the primitive numeric types and boolean.


2) Overriding equals(...) to return true for equivalent object states is orthogonal to implementing Comparable, granted that a class that implements Comparable must always override equals(...) for consistency, unless the implementation of Comparable has to fulfill some extremely rare (aka wierd ) requirement.

The reverse, as implied in your statement, is not true. Comparing String or any other objects for equality of state using equals(...) does not in any way depend on the class implementing Comparable.


3) More strictly, it checks the equality of the references. Two references (aka reference variables) are equal if both refer to the same object. (Two primitive variables are equal if they contain the same value, but everyone knows that )


4) Very useful especially in event driven programming where the event holds a reference to the object that created/dispatched it. For example, in a listener that's added to several GUI components to perform the same action, but only on the component that triggered the event.


Relevant, and well explained.

db

Wow, pwnd... To be fair, I wrote that at like 11pm.

Either way,
1) Primitive! I was looking for that word but couldn't remember it.
2) I knew classes that don't implement Comparable can be compared, but I was unsure the details so I decided not to go in depth with it since it was irrelevant for Evelina for the time being.
3) I've got nothing for this one. Learning a little more every day.
4) I can't believe I didn't notice that. I compare GUI elements ALL THE TIME in my Listeners.

Originally Posted by Evelina

Hello, I am writing a code that its showing the process of renewing your mail address when you move.

this is part of the program that i need help on

public class NewDataEntry 
	{
		private String name;
		private String oldAddress;
		private String newAddress;
 
 
// where are the values of name, oldAddress, and newAddress initialized?  if nowhere, then you'll be comparing null String anyway and will likely get a Null Pointer Exception
 
		// a method that compares the old and the new address. if the address is the same the program     goes through it
		// if they are not the same it's false, and it needs the new address.
 
 
		// a subclass for a new entry if the addresses are not the same.
 
		public String getName()
		{
			return name;
		}
		public String getoldAddress()
		{
			return oldAddress;
		}
		public String getnewAddress()
		{
			return newAddress;
		}
 
public boolean isTheSame()
{
if (getOldAddress().equals(getNewAddress())
{
return true;
}
 
else
return false;
}
 
if (!isTheSame())
{
Subclass sub = new Subclass();
// whatever you wanted to do with the subclass.  It won't do anything unless call its methods.  
}
 
else
{
// whatever else you wanted to do
}
	}

i need a method that it will compare the oldAddress with the newAddress, when it is inputed.
if the new address that is inputed its the same thing as we have on file than the program skips that method but if its not, it has to compare and replace it with the new one....Im having hard time getting this ...can someone guide me?

Compare to in what way? String implements an interface called Comparable that has a method called compareTo(). Not sure if that's what you were looking for.

Java 2 Platform SE v1.3.1: Class String

However, if you're looking for exact equality, use .equals.

I showed how to do it above by editing your code.

Every time I search, it seems to come to the old version of Java, that's what the first entry on the search engine results page shows me.

I think. How often do they update?

Have they created a handy file that will use a JFileChooser and help save and load it for you so you don't have to fiddle with that nightmare by yourself?

Also, by any chance did they define the String class by having a String be

private Vector <Character> cVector;
public String(cVector)
{

}

That would also make a getCharAt(int i) a whole lot easier if it was defined using characters. Either an array or a Vector.