Preparing Java 7 Certifications

Oracle Certificate AssociateJava 7

My Personal Note

This PPT is NOT a Java 7 course is a set of concepts to MEMORIZE to take the OCA7

Prerequisites: java expert

Bibliography

OCA Java SE 7 Programmer I Certification Guide PREPARE FOR THE 1Z0-803 EXAM MALA GUPTA

Manuale di Java 7 C. De Sio Cesari HOEPLI

Oracle certified associate java se 7 programmer study guide Richard Reese PACKT

OOP basic


(Default) Constructor

A default constructor is the one that has no arguments and is provided automatically for all classes. This constructor will initialize all instance variables to default values.

However, if the developer provides a constructor, the compiler's default constructoris no longer added.

The developer will need to explicitly add a default constructor.

It is a good practice to always have a default, no-argument constructor.

Legal vs Illegal

Legalclass MyClass public void MyClass(String name){}

Having a method with the same name of a constructor, but it is NOT a constrcutor

Legalclass MyClass

{name=...

} //init block

Legalclass MyClass public MyClass(String name){this(name,another sring)}

public MyClass(String name, String surname){...

Calling a constructor within another constructor

Classes

Compile error

abstract final class ..

class public ..

Visibility precendence

public > protected > default > private

Classes modifier (inner excluded)

public and default

Interfaces

An interface is similar to an abstract class.

It is declared using the interface keyword and consists of only: abstract methods and

final variables.

Note: final keyword is illegal on interface


Methods

The signature of a method consists of:The name of the method

The number of arguments

The types of the arguments

The order of the arguments

Notice that: the definition of a signature does not include the return type.

pacakge scoped cannot be visible by any class outside the (also inheriting)

private void setAge(int age) {age = age;}

This code would not have the intended consequences of modifying the age instance variable. The parameters will have "precedence" over theinstance variables.

Private void myMethod(int x) {

}

Calling myMethod without parameter (myMethod()) we pass an empty array.

Widening

PrecedenceWidening

Boxing

Varargs

Variables

Variables can be classified into the following three categories:Instance variables

Static variables

Local variables

Identifiers are case-sensitive and can only be composed of: Letters, numbers, the underscore (_) and the dollar sign ($)

Identifiers may only begin with a letter, the underscore or a dollar sign

Examples of valid variable names include: NumberWheels, OwnerName, Mileage, _byline, NumberCylinders, $newValue, _engineOn

Numbers

Number of digits Recommended data typeLess than 10 Integer or BigDecimal

Less than 19 Long or BigDecimal

Greater than 19 BigDecimal

When using BigDecimal, it is important to note the following:Use the constructor with the String argument as it does a better job at placing the decimal point

BigDecimal is immutable

The ROUND_HALF_EVEN rounding mode introduces the least bias


Floating point (exp)

float num1 = 0.0f;

System.out.println(num1 / 0.0f);

System.out.println(Math.sqrt(-4));

System.out.println(Double.NaN + Double.NaN);

System.out.println(Float.NaN + 2);

System.out.println((int) Double.NaN);

System.out.println(Float.NEGATIVE_INFINITY);

System.out.println(Double.NEGATIVE_INFINITY);

System.out.println(Float.POSITIVE_INFINITY);

System.out.println(Double.POSITIVE_INFINITY);

System.out.println(Float.POSITIVE_INFINITY+2);

System.out.println(1.0 / 0.0);

System.out.println((1.0 / 0.0) - (1.0 / 0.0));

System.out.println(23.0f / 0.0f);

System.out.println((int)(1.0 / 0.0));

System.out.println(Float.NEGATIVE_INFINITY == Double.NEGATIVE_INFINITY);

NaN

NaN

NaN

NaN

0

-Infinity

-Infinity

Infinity

Infinity

Infinity

Infinity

NaN

Infinity

2147483647

True

Strictfp abide the IEEE standard

Boxing and Unboxing and equals

Autoboxing is the automatic conversion of primitive data types into their corresponding wrapper classes. This is performed as needed so as to eliminate the need to perform trivial, explicit conversion between primitive data types and their corresponding wrapper classes.

Unboxing refers to the automatic conversion of a wrapper object to its equivalent primitive data type. In effect, primitive data types are treated as if they are objects in most situations.


Literals

Literal constants are simple numbers, characters, and strings that represent aquantity. There are three basic types:Numeric

Character

Strings

Java 7 added the ability to uses underscore characters (_) in numeric literals.NOTE

consecutive underscores are treated as one and also ignored

underscores cannot be placed:At the beginning or end of a number

Adjacent to a decimal point

Prior to the D, F, or L suffix

Numeric literals that contain a decimal point are by default double constants.

Numeric constants can also be prefixed with a 0x to indicate the number is a hexadecimal number (base 16).

Numbers that begin with a 0 are octal numbers (base 8).

Remember String pool

True returnString a=hello;String b=hello;a==b; hel+lo ==b; hello ==a; hello.replace('l','l')==a

False return

String a=hello;String b=new String(hello);hel.concat(lo) ==a; hel+lo ==b; hello ==b;heLLo.replace('L','l')==a

Character

Escapes\a alert

\b backspace

\f form feed

\n new line

\r carriage return

\t horizontal tab

\v vertical tab

\\ backslash

\? question mark

\' single quote

\" double quote

\ooo octal number

\xhh hexadecimal number

Character: This deals with the manipulation of character data

Charset: This defines a mapping between Unicode characters and a

sequence of bytes

CharSequence: In this, an interface is implemented by the String,

StringBuffer and StringBuilder classes defining common methods

StringTokenizer: This is used for tokenizing text

StreamTokenizer: This is used for tokenizing text

Collator: This is used to support operations on locale specific strings

The String, StringBuffer, and StringBuilder classes

MutableSynchronized

Stringnono

StringBuilderyesno

StringBufferyesno

Operators

TIPSTotal += 2; // Increments total by 2

Total =+ 2; // Valid but simply assigns a 2 to total!


String equals (intern)

String firstLiteral = "Albacore Tuna";String secondLiteral = "Albacore Tuna";String firstObject = new String("Albacore Tuna");

if(firstLiteral == secondLiteral) { //RETURN TRUE..

If !(firstLiteral == firstObject) { //RETURN TRUE...

String make an intern constant equaks fo every instance


Operators

=> is not legal

5 < x < 15 is not legal

Do not confuse the bitwise operators, &, ^, and | with the corresponding logical operators && and ||. The bitwise operators perform similar operations as the logical operators, but do it on a bit-by-bit basis.

Mistakes

if (1>2 && 2>1 | true) {System.out.println("1");} else {System.out.println("2");

}

Th results is 2 since the | operator is evaluated before the &&

(1>2 && 2>1 | true)

Is (1>2 && (2>1 | true))

If short circuit

If (a == b && c==d)

If (a == b || c==d)

Java will evaluate only the first expression if

a!=b

a==b

To avoid short circuit use the bitwise operator

Sometimes the short circuit could be avoided (eg. When you evaluate a method and you expect the method will be called)

If mistakes

if (limit > 100)if (stateCode == 45)limit = limit+10;

elselimit = limit-10;

if (isLegalAge)System.out.println("Of legal age");

elseSystem.out.println("Not of legal age");

System.out.println("Also not of legal age");

In the example the last print is executed owever

In the example else is referred to the second if

Switch tips

switch (x) {case 4:

case 5:cost = weight * 0.23f;

break;

case 6:cost = weight * 0.23f;

break;

default:cost = weight * 0.25f;

}

switch (zone) {

case "East":cost = weight * 1.09;

break;

case "NorthCentral":cost = weight * 1.1;

break;

default:cost = weight * 1.2;

}

It works only on Java 7

It raise exception when zone is null. Consult java.util.Objects

integer data types include byte, char, short, and int. Any of these data types can be used with an integer switch statement. The data type long is not allowed.

arrays

array of objects uses a reference variable

array are intialized to default primitive value or null if object

For each loop works

for(int j : numbers) {...;

}

Bidimensional array (they are arrays of arrays)

int coords[][] = new int[ROWS][COLS];or

coords = new int[ROWS][];

coords[0] =new int[COLS];

To compare arraysArrays.equals(arr1,arr2)

Arrays.deepEquals(arr1,arr2) //for object simce use equals object method

System.arraycopy method Performs a shallow copy

Arrays.copyOf method Performs a deep copy of the entire array

Arrays.copyOfRange method Performs a deep copy of part of an array

clone method Performs a shallow copy

Legal vs Illegal

Legal

int[] a, b[]; //b is a 2D array

int[] a[]; //2D array

Illegalint[] z = new int[];

Illegal

int[] a = new int[2]{1.0,2.0}

int[] a = {1.0,2.0}

int[] a = new int[]{1.0,2.0}

Arrays class

int arr1[] = new int[5];

Arrays.fill(arr1,5); // fill the integer array with the number 5

Arrays.toString(arr1)); //return array data

Arrays.deepToString(arr2); // return also the array of aray data

Arrays.asList

The asList method takes its array argument and returns a java.util.List object representing the array. If either the array or the list is modified, their corresponding elements are modified.

Iterator of ArrayList

ListIteratornext: This method returns the next element

previous: This method returns the previous element

hasNext: This method returns true if there are additional elements that follow the current one

hasPrevious: This method returns true if there are additional elements that precede the current one

nextIndex: This method returns the index of the next element to be returned by the next method

previousIndex: This method returns the index of the previous element to be returned by the previous method

add: This method inserts an element into the list (optional)

remove: This method removes the element from the list (optional)

set: This method replaces an element in the list (optional)

Iteratornext: This method returns the next element

hasNext: This method returns true if there are additional elements

remove: This method removes the element from the list (UnsupportedOperationException exception should be thrown)

Other colllection elementsSet : HashSet, TreeSet

List: ArrayList, LinkedList

Map: HashMap, TreeMap

The ArrayList class is not synchronized.When an iterator is obtained for a ArrayList object, it is susceptible to possible simultaneous overwrites with loss of data if modified in a concurrent fashion. When multiple threads access the same object, it is possible that they may all write to the object at the same time, that is, concurrently.

To sort array listCollections.sort(arr);

for

For loop

for (;;)

could be rewritten as

for (;;) {if ! break

..

}

Legal: for(;;) ;

Legal: for (int i=0, j=0; i

Education

Preparing Java 7 Certifications