One possible objection is that it produces a file in machine-readable form instead of human-readable. It's nice to be able to read the data in the file directly. It also ties the file very tightly to the PhoneDirectory class. It might be nice to be able to use the same data in other programs that use different classes to store the directory data. Instead, I designed a text-file format. The first line of the data file specifies the number of entries in the phone directory.
After that, there are two lines for each entry. The first line is the name and the second is the associated number. My PhoneDirectory class contains two instance methods for reading and saving data.
It's not clear that the PhoneDirectory class is the best place for these methods. Maybe the saving and reading should be done entirely in the main program. However, my PhoneDirectory class provides no way for the main program to get a list of all entries from the directory, so there is no way for the main program to save that list in a file.
Arguably, it might have been preferable to add such a method to the PhoneDirectory class. Here are the methods. The essential point is that the load method must be able to read data in the exact format that is written by the save method. Using these methods, the following code could be used to load a phone directory from a file named fileName :.
In my program, the data is stored in a file named "phone. If the file does not exist, the program offers to create a new, empty phone directory. Otherwise, it tries to read the phone directory data from the file.
Here is the code that I actually use in my program to load the phone directory:. In this simple implementation, both the names and the numbers are stored as strings. The names and numbers must be non-null strings, but no attempt is made to ensure that the values make sense. Comparison of names is in all cases case-insensitive. A given name cannot occur more than once in the directory. The instance methods throw IllegalArgumentExceptions when the rules are violated. The instance methods load and save are provided for loading the data for the directory from a stream and for saving the data to a stream.
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The phone number associated with the name names[i] is numbers[i]. These arrays will grow, as necessary, to accommodate as many entries as are added to the directory. The variable count keeps track of the number of entires in the directory. Note that PrintWriters do not throw exceptions. If it is, an IllegalArgumentException is thrown. The directory is implemented as an object belonging to the class PhoneDirectory.
This object keeps a list of names and associated numbers.limitless.solidhosting.pro/sitemap.xml
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A name can occur at most once in the directory. When the program is loaded, the data for the directory is loaded from a file. If the data is changed while the program is running, then the file is rewritten with the changed data before the program terminates. If no file with the given name exists when the program is run, the user is given the option of creating a new, empty phone directory file.
The user can perform a sequence of operations on the directory chosen from this list: Look up a number, add an entry, delete an entry, or modify an entry. This continues until the user chooses to exit from the program. This routine might terminate the program if an error occurs when the attempt is made to end the data. Repeat until the user selects the "Exit from this program" operation.
Each of the other four commands is carried out by calling a subroutine. Look up a phone number" ; TextIO. Add an entry to the directory" ; TextIO. Delete an entry from the directory" ; TextIO. In computer programming, integers such as , and floating-point numbers such as 1. Integers are representated in a so called 2's complement scheme as illustrated. The remaining bits represent the magnitude of the integers. For positive integers, the magnitude is the same as the binary number, e.
Negative integers require 2's complement conversion. Floating-point numbers are represented in scientific form of Fx2 E , where Fraction F and Exponent E are stored separately. For example, to store Integers and floating-point numbers are operated differently using different hardware circuitries.
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Integer operations are straight-forward. For example, integer additon is carried out as illustrated:. It is obvious that integer operations such as additon is much faster than floating-point operations. Furthermore, integer are precise. All numbers within the range can be represented accurately. On the other hand, floating-point are NOT precise, but close approximation. This is because there are infinite floating-point numbers in any interval e.
Not ALL numbers can be represented using a finite precision bit float or bit double. Read " Data Representation - Integers, Floating-Point Numbers and Characters " if you wish to understand how the numbers and characters are represented inside the computer memory.
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In brief, It is important to take note that char '1' is different from int 1 , byte 1 , short 1 , float 1. They are represented differently in the computer memory, with different precision and interpretation. They are also processed differnetly. There is a subtle difference between int 0 and double 0. Furthermore, you MUST know the type of a value before you can interpret a value. For example, this bit-pattern " " cannot be interpreted unless you know its type or its representation. The following program can be used to print the maximum , minimum and bit-length of the primitive types.
Beside the 8 primitive types, another important and frequently-used type is String. A String is a sequence of characters texts such as "Hello, world". String is not a primitive type this will be elaborated later. In Java, a char is a single character enclosed by single quotes e. As a programmer, YOU need to decide on the type of the variables to be used in your programs. Most of the times, the decision is intuitive.
For example, use an integer type for counting and whole number; a floating-point type for number with fractional part, String for text message, char for a single character, and boolean for binary outcomes. Example Variable Names and Types : Paul has bought a new notebook of "idol" brand, with a processor speed of 2. He has chosen service plan 'C' among plans 'A', 'B', 'C', and 'D', plus on-site servicing but did not choose extended warranty.
Identify the data types and name the variables. Exercise Variable Names and Types : You are asked to develop a software for a college. The system shall maintain information about students.