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Java Programing. PSC 120 Jeff Schank. Let’s Create a Java Program. Open Eclipse Create a project: File -> New -> Java Project Create a package: File -> New -> Package Create a Class: File -> New -> Class. How to say “Hello World!”. Let’s Add Some Numbers. Let’s Format the Results.

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Java programing

Java Programing

PSC 120

Jeff Schank


Let s create a java program
Let’s Create a Java Program

  • Open Eclipse

  • Create a project: File -> New -> Java Project

  • Create a package: File -> New -> Package

  • Create a Class: File -> New -> Class





Classes
Classes

  • Let’s create another class called “Agent”

  • File -> New -> Class


Data

  • Now, let’s add some data—in this case a vocabulary


Methods
Methods

  • Now, let’s add a method




Variables and their types
Variables and Their Types

  • As we just saw, we define the objects that will interact in our simulation by defining classes

  • Once a class is completely defined, then it can be instantiated many times

    • For example, we could define a class called “Person” and then make 1000 persons that interact in our simulation.

  • Classes have members that occupy fields in a class

  • A class can have indefinitely many fields and a field is either occupied by variables or methods

  • When defining classes, I prefer to place the variables first and methods second in a class, but Java does not care how they are ordered

  • Let’s look at some of the types of variables we can define in a class.


Example myclass
Example MyClass


Access modifiers
Access Modifiers

  • Variables (and methods) have specifications for how they are accessed

  • There are four types of access modifiers: no explicit modifier, public, private, and protected.

    • public modifier—the field is accessible from all classes.

    • private modifier—the field is accessible only within its own class.

    • protected modifier—the field is accessible within its own class, package, and subclass.

    • no explicit modifier—the field is accessible within its own class and package


Methods1
Methods

  • Methods specify how objects do things (how they behave)

  • Methods also specify how objects interact with other objects

  • Methods have at least five features:

    • Modifiers—such as public, private, and others listed above.

    • The return type—the data type of the value returned by the method, or void if the method does not return a value.

    • The method name—the rules for field names apply to method names as well, but the convention is a little different.

    • The parameter list in parenthesis—a comma-delimited list of input parameters, preceded by their data types, enclosed by parentheses, (). If there are no parameters, you must use empty parentheses.

    • The method body, enclosed between braces—the method’s code, including the declaration of local variables, goes here.


Example method
Example Method

4. Parameter List

3. Method Name

2. Return Type

5. Body

1. Modifier


Example method1
Example Method

4. Parameter List

3. Method Name

2. Return Type

5. Body

1. Modifier


Example method2
Example Method

4. Parameter List

3. Method Name

2. Return Type

5. Body

1. Modifier


Logical operators
Logical Operators

  • && means roughly “and”

  • || means roughly “or”

  • == means roughly “equals”

  • ! means roughly “not”

  • != means roughly “not equal to”

  • > means “greater than”

  • >= means “greater than or equal to”

  • < means "less than”

  • <= means "less than or equal to"




Arithmetic operators
Arithmetic Operators

  • + Additive operator but it is also used for String concatenation.

  • – Subtraction operator

  • * Multiplication operator

  • / Division operator



If then statement
If-then Statement

Conditions

Body



For statements
For Statements

  • Probably, the next most commonly used control statement is the for statement.

  • For control statements are one of several control statements that allow you to perform a number of operations over and over again for a specified number of steps (the others are while and do-while).

  • For statements typically have three statements as arguments and then a body that is repeated (there are variations on this theme).


A common form
A common form

Arguments

Modifier

Body



Another example
Another Example

The maximum value for an integer is 2147483647

But, since it does not stop at this value, it would generate an error.



Scope of a variable
Scope of a Variable

  • The scope of a variable is the region of a program within which, a variable can be referenced.

  • In Java, the largest scope a variable can have is at the level of the class.

  • So, if variables are declared in a class field, they can be referenced anywhere in the class including inside methods.





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