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The if and else statements allow a block of code or a single statement to be ither executed or bypassed depending upon the result of a comparison operation. They are an essential part of Java “flow control” by which execution may proceed along alternate logic paths within a program.
The if statement 1. Identifies a single statement or a block of statements to be executed if an expression evaluates to true. 2. Have two forms. The general syntax is either of the following: if (expression) statement; or if (expression) { statements; } The first form is often referred to as a “single statement if”. …
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The else statement 1) Defines an alternative and mutually exclusive logic path to be followed if the preceding if statement expression evaluates to false 2) Must always be paired with, and follow, an if statement. It can never be coded separately 3) Have two forms. The general syntax is either of the following: else statement; …
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Switch statements Flow control with if and else statements gets cumbersome when a variable must be tested for a large number of possible values, such as a menu selection that permits the user to enter an integer from 1 to 20. The solution to this problem is the switch statement. The switch statement 1) Specifies …
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The ability to “loop” by executing one or more statements repetitively is an important part of programming. Loops reduce the number of statements a programmer must code and result in a smaller, more memory efficient program. In Java, looping is performed using the for, while, and do-while statements.
The for statement 1) It is useful when the number of passes (iterations) can be predetermined The general syntax for (initialization; condition; update) { statements; } where: initialization – represents the declaration of one or more local variables of the same data type. When loop processing is complete, all such variables are destroyed. condition – …
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The while statement 1) It Defines a block of code to be executed as long as a particular condition is met. The condition is tested prior to each iteration. It has the general syntax while (condition) { statements; } where condition represents a binary expression that, if true, permits an iteration of the loop. If …
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1) It defines a block of code to be executed as long as a particular condition is met. The condition is tested at the end of each iteration. It always guaranteed at least one pass through a do-while loop. syntax do { statements; } while (condition); where condition represents a binary expression that, if true, …
Using break and continue At times, it is desirable to exit from a loop or short-circuit the current iteration of a loop. The break and continue statements make it happen.
The break statement 1) Can only appear within a loop or a switch statement. 2) Causes an immediate exit from a loop structure before the test condition is met. Once a break statement is encountered, the loop immediately terminates, skipping any remaining code. For example, for (int x = 0; x < 10; x++) { …
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The continue statement 1) Can only appear within a loop. 2) Skips all remaining statements within the loop and resumes with the next iteration. For example, for (int x = 0; x < 10; x++) { if (x == 5) continue; else System.out.print(” ” + x); } will short-circuit when x takes on a value …
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Definition: A class is a blueprint or prototype that defines the variables and methods common to all objects of a certain kind.
Objects provide the benefit of modularity and information hiding. Classes provide the benefit of reusability. Software programmers use the same class, and thus the same code, over and over again to create many objects.
To define a class, we use the class keyword and the name of the class: class MyClassName { … } By default, classes inherit from the Object class. If this class is a subclass of another specific class (that is, inherits from another class), use extends to indicate the superclass of this class: class myClassName …
Class using constructor Here’s a of SimpleRectangle, called Rectangle, that contains four constructors, a method to “move” the rectangle, a method to compute the area of the rectangle, and a finalize method to provide for clean up: public class Rectangle { public int width = 0; public int height = 0; public Point origin; // …
An object is a distinct instance of its class (an actual occurrence). It has its own set of variables (known as “instance variables”) and methods (known as “instance methods”). When called, an object’s instance methods automatically act upon its instance variables Java program creates many objects from a variety of classes. These objects interact with …
Like other variable declarations, object declarations can also appear alone, like this: Rectangle rect; Declarations notify the compiler that you will use name to refer to a variable whose type is type. Declarations do not create new objects. Rectangle rect does not create a new Rectangle object, just a variable named rect to hold a …
The classes can provide one or more constructors to initialize a new object of that type. We can recognize a class’s constructors because they have the same name as the class and have no return type. Here are the declarations for Rectangle’s constructors: public Rectangle(Point p) public Rectangle(int w, int h) public Rectangle(Point p, int …
Assume we create a rectangle named rect as described in the previous section. To move rect to a new location, we would write: rect.origin = new Point(15, 30); This statement moves the rectangle by setting its point of origin to a new position. rect.origin is the name of rect’s origin variable. The Rectangle class has …
To move rect to a new location using its move method, we write this: rect.move(15, 30); This Java statement calls rect’s move method with two integer parameters, 15 and 30. It moves the rect object because the rect method assigns new values to origin.x and origin.y, and is equivalent to the assignment statement used previously: …