session 1- language fundamentals

7/31/2019 Session 1- Language Fundamentals

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Core Java Session 1- LanguageFundamentals

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Java Certification


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Introduction to Java: J2SE


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Session 1Language Fundamentals

Operators and Assignments

(Chapter 1+2 in [Complete Java 2 Certification StudyGuide, 5th Edition] text book)


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Objectives (1)

Language Fundamentals Source Files

Keywords and Identifiers

Primitive Data Types

Literals

Arrays

Importing

Class Fundamentals

Argument Passing: By Reference or by Value

Garbage Collection


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Objectives (2)

Operators and Assignments Overview of the Java Operators

Evaluation Order

The Unary Operators

The Arithmetic Operators

The Comparison Operators

The Bitwise Operators

The Short-Circuit Logical Operators

The Conditional Operator

The Assignment Operators


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Source Files

Must end with the .java extension

If a public class is present, the class nameshould match the unextended filename.

Three top-level elements known ascompilation units. If they are present, thenthey must appear in the following order:

1.Package declaration2.Import statements

3.Class, interface, and enum definitions


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Keywords

Java Keywords and Reserved Words


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Identifiers

An identifieris a word used by a programmer

to name a variable, method, class, or label.

An identifier must begin with a letter, a dollar

sign ($), or an underscore (_); subsequent

characters may be letters, dollar signs,

underscores, or digits.


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Aprimitive is a simple non-object data type thatrepresents a single value. Javas primitive data typesare.

boolean

char

byte

short

int

long

float

double


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Literals

A literalis a value specified in the program source, asopposed to one determined at runtime.

Literals can represent primitive or string variables

and may appear on the right side of assignments orin method calls. You cannot assign values into literals,so they cannot appear on the left side ofassignments.

For example:String s = Characters in strings are 16-bit Unicode.;Char c=w;


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Arrays (1)

A Java arrayis an ordered collection of primitives,

object references, or other arrays.

Java arrays are homogeneous: except as allowed by

polymorphism. To create and use an array, you must follow three

steps:

1. Declaration

2. Construction

3. Initialization


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Arrays (2)

type[] identifier; //declaration

identifier=new type[size]; //construction


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Multi-dimension Arrays

int[][] myInts = new int[3][4];


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Importing

Import statement brings name into thesource files namespace. (A namespace is a kindof placenot a physical place, but an abstract place

such as a directory or a source file

that containsitems with unique names).

Syntax:

import packageName.*;

or

import packageName.ClassName;


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static import

Without static imports, you have to do the following:

import java.awt.Color;

myColor = Color.GREEN; With a static import, you can import the name

GREEN into your namespace:

import static java.awt.Color.GREEN;

myColor = GREEN;


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Class Fundamentals(1)

Class Paths

When the Java compiler or the VirtualMachine needs a classfile, it searches all the

locations listed in its classpath. The classpathis formed by merging:

CLASSPATH environment variable and

-classpath or -cp command line arguments. The members of a classpath may be

directories or jar files.


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The main() Method

The main() method is the entry point for standaloneJava applications.

The signature for main() ispublic static void main(String[] args)

args is that the user might have entered on thecommand line.

For example, consider the following command line:java Mapper France Belgium


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Variables and Initialization

Java supports variables of three different lifetimes:

Member variable A member variable of a class is createdwhen an instance is created, and it is destroyed when the

object is destroyed. Automatic variable An automatic variable of a method is

created on entry to the method and exists only duringexecution of the method.

Class variable A class variable (also known as a static variable)is created when the class is loaded and is destroyed when theclass is unloaded.


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Argument Passing: By Reference

or by Value When Java passes an argument into a method

call, a copyof the argument is actually passed.

This is also true when the argument to bepassed is an object rather than a primitive.

Why? !!!


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Object Reference

Java programs do not deal directly withobjects. When an object is constructed, theconstructor returns a valuea bit pattern

that uniquely identifies the object. This valueis known as a reference to the object.

For example:

Student s;

s = new Student(11078,John);


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How to Create a Reference to a

Primitive?

Simply pass an array of one primitive element

over the method call.


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Garbage Collection (1)

Most modern languages permit you to allocate data

storage during a program run. In Java, this is done

directly when you create an object with the new

operation and indirectly when you call a method thathas local variables or arguments.

Method locals and arguments are allocated space on

the stack and are discarded when the method exits,

but objects are allocated space on the heap and havea longer lifetime.


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Garbage Collection (2)

In Java, you never explicitly free memory that you

have allocated; instead, Java provides automatic

garbage collection.

The runtime system keeps track of the memory thatis allocated and is able to determine whether that

memory is still useable. How?

Out of scope

or

Assign to null


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Operators and Assignments

Overview of the Java Operators

Evaluation Order

The Unary Operators

The Arithmetic Operators The Comparison Operators


The Short-Circuit Logical Operators

The Conditional Operator

The Assignment Operators


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Overview of the Java Operators

Operators in Java, in Descending Order of Precedence

Shifts bits of op1 right bydistance op2; fills with 0

bits on the left side


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Operators in Java, in Descending Order of Precedence ...

if (x) {a = b;

}

else {a = c;}Replace with:a=x?b:c;


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Evaluation Order

In Java, the order of evaluation of operands in anexpression is fixed.

Consider this code fragment:

1. int [] a = { 4, 4 };

2. int b = 1;

3. a[b] = b = 0

It is generally better style to keep expressions simple and touse redundant bracketing to make it clear how any particularexpression should be evaluated.


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The Arithmetic Operators Problems

Arithmetic Error Conditions

Integer division by zero

Arithmetical incorrect result

NaN (Float.NaN, Double.NaN):non-ordinal for

comparisons.

Overflow/Underflow


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Comparison Operators

Primitive types: == and !=

Reference types (object): equals() method


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Core Java Session 1- LanguageF d t l

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Summary

Language Fundamentals Source Files

Keywords and Identifiers


Literals

Arrays

Importing

Class Fundamentals

Argument Passing: By

Reference or by Value Garbage Collection

Q&A

Operators and Assignments Overview of the Java Operators

Evaluation Order

The Unary Operators

The Arithmetic Operators

The Comparison Operators


The Short-Circuit Logical

Operators

The Conditional Operator The Assignment Operators

session 1- language fundamentals

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