[PDF] Algoritmos y Estructuras de Datos: [0.3cm] Introducción





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Algoritmos y Estructuras de Datos: [0.3cm] Introducción

Repaso Conceptos de Programación en Java Java tiene sus reglas de visibilidad establecidas ... ¿es upcasting o downcasting?



Algoritmos y Estructuras de Datos: [0.3cm] Introducción

Repaso Conceptos de Programación en Java Java tiene sus reglas de visibilidad establecidas ... ¿es upcasting o downcasting?



Programación en Java

Java. 3. Clases Wrapper. • Los tipos de datos primitivos no son objetos y por tanto no pueden acceder a los métodos de Java. 63. Upcasting y Downcasting.



Interfaces Java interface Notes Why an interface construct? Example

Upcasting and Downcasting. • Applies to reference types only. • Used to assign the value of an expression of one. (static) type to a variable of another 



CECS 277 Midterm 1 Review

Upcasting and downcasting. What is the difference between up-casting and down-casting? Casting in java means converting from type to type.



Conversioni di oggetti in Java

Conoscere il tipo di un oggetto. CHE COSA DOVRAI STUDIARE. La conversione dei tipi. + Upcasting. Downcasting. > La conversione di un vettore.



Upcast - downcast

class C extends B { void f3(). {System.out.println("f3");} }. OK: upcast implicito. NO: downcast illecito (runtime error) java.lang.ClassCastException 



GUÍA DOCENTE

utilizando de forma eficiente las clases de la API que proporciona Java. Alcanzar estos objetivos implica 3.2 Upcasting y Downcasting. 3.3 Arrays.



GL2 : Problématique du Développement Logiciel

2- en Java si vous ne spécifiez pas de lien d'héritage



Week 10(19) OOSD1 Java lab exercises: Casting Abstract class

Exercise 1: Upcasting and Downcasting. Upcasting: casting a subtype to a supertype upward to the inheritance tree. Downcasting: casting from base class to 



What is Upcasting and Downcasting in Java

Downcasting is casting to a subtype downward to the inheritance tree Let’s see an example: Here we cast the Animal type to the Cat type As Cat is subclass of Animal this casting is called downcasting Unlike upcasting downcasting can fail if the actual object type is not the target object type For example:

  • Upcasting

    Upcasting is a type of object typecasting in which a child object is typecasted to a parent class object. By using the Upcasting, we can easily access the variables and methods of the parent class to the child class. Here, we don't access all the variables and the method. We access only some specified variables and methods of the child class. Upcas...

  • Downcasting

    Upcasting is another type of object typecasting. In Upcasting, we assign a parent class reference object to the child class. In Java, we cannot assign a parent class reference object to the child class, but if we perform downcasting, we will not get any compile-time error. However, when we run it, it throws the "ClassCastException". Now the point i...

What is upcasting and downcasting of objects in Java?

Object Typecasting can be of two types, depending on whether we are converting from parent type to child or going in the other way. In this tutorial, we will learn about Upcasting and Downcasting of objects in Java. The process of casting an object of child class to the parent class is called Upcasting.

What is typecasting in Java?

A process of converting one data type to another is known as Typecasting and Upcasting and Downcasting is the type of object typecasting. In Java, the object can also be typecasted like the datatypes. Parent and Child objects are two types of objects.

What is implicit upcast in Java?

The purpose of an implicit upcast (for a Java object type) is to "forget" static type information so that an object with a specific type can be used in a situation that requires a more general type. This affects compile-time type checking, not runtime behavior.

Can we perform upcasting and downcasting implicitly?

We can perform Upcasting implicitly or explicitly, but downcasting cannot be implicitly possible. Upcasting is a type of object typecasting in which a child object is typecasted to a parent class object. By using the Upcasting, we can easily access the variables and methods of the parent class to the child class.

  • Past day

Algoritmos y Estructuras de Datos:

Introduccion

Guillermo Roman Dez

groman@.upm.es

Universidad Politecnica de Madrid

Curso 2015-2016

Guillermo Roman, UPM AED: Introduccion 1/42

Repaso Conceptos de Programaci

on en JavaExpresiones, constantes, metodos, comandos, ...

Variables, declaracion e inicializacion, ...

Bloques de codigo,

ujo de control, condiciones, bucles, ...

Objetos,new, campos, herencia, interfaces, ...Tipos basicos, operadores aritmeticos, operadores logicos, ...

Arrays, declaracion y acceso mediante ndices, ...

Excepciones,try-catch-finally, ...

Guillermo Roman, UPM AED: Introduccion 2/42

Asignaci

on y variablesLas variables tienen untipoy unambitoDeclaracion de variables:

Atributos de clase!Visibles en toda la clase (o mas...)Parametros de los metodos!Visibles en todo el metodoLas variables locales!Visibles en suambitoInicializacion por defecto

Si son de tipo primitivo!0, 0.0, 'n0'Si son de tipo referencia!nullAsignacion de variables:l-valuevsr-value

int x ,y; y = 7; x = y = 3;

V alor

d e x e y while ( (x=y/2)! =0 ){ ...}

Guillermo Roman, UPM AED: Introduccion 3/42

EJERCICIO: Asignaciones

1publics taticv oidm ain(String[ ]a rgs){

2intv 1= 3 ;

3intv 2= 5 ;

4intv 3;

5

6v3 = v1;

7v1 = v2;

8v3 = v1 = 6;

9v3 = 6 = v5;//E rror

10v3 = 7;

11}Ejercicio

>cuales son los valores de las variables despues de ejecutar cada punto de programa?

Guillermo Roman, UPM AED: Introduccion 4/42

Ambito de las variablesJava tiene sus reglas de visibilidad establecidas Otros lenguajes pueden tener sus propias reglas de visibilidad Puede ocurrirshadowing: Si hay dos variables que se llaman igual una puedeocultara la otra public c lass C { int x ; public C ( int x ){ x = x ;} //? ? public v oid m 1( int x ){ for int x = 1 ;x < 1 0;x ++)//? ? x++; if ( x< 0 ){ int x = 1 ;//? ? this .x= x ;//? ? public v oid m 2( int c ){ x = c ;} //? ?

Guillermo Roman, UPM AED: Introduccion 5/42

Paso de Par

ametros por ValorUn ejemplo de codigo para intercambiar dos variables: int x = 5 ; int y = 4 ; c odigo d el i ntercambio swapping int t mp= x ; x = y; y = tmp;Pregunta >Podemos hacer esto llamando a un metodo que recibaxeycomo parametros?

Guillermo Roman, UPM AED: Introduccion 6/42

Paso de Par

ametros por Valor public s tatic v oid s wap( int a , i nt b ){ int t mp= a ; a = b; b = tmp; public s tatic v oid m ain(String[ ]a rgs){ int x = 5 ; int y = 7 ; swap(x,y);

System.out.println(x +"" + y);

}Pregunta >Que saldra por pantalla?

Guillermo Roman, UPM AED: Introduccion 7/42

Ejercicio Variables

Ejercicio

Dibujar las variables durante la ejecucion

public s tatic v oid m ain(String[ ]a rgs){ int a = 3 ; int b = 3 ; a = 2; int c = 3 ; int d = c ; c = 2; int e = 3 ; e = 2; int d = e ;

Guillermo Roman, UPM AED: Introduccion 8/42

Evaluaci

on de expresionesJava evalua las expresionesen cortocircuitoSi tenemos un&&corta en el momento en el que no se cumpla

una condicion!evalua afalse v != n ull & &v [i]= =0 Si tenemos un||corta en el momento en el que se cumpla una condicion!evalua atrue v == n ull | |v [i]= =0

Guillermo Roman, UPM AED: Introduccion 9/42

Arrays (vectores)

Podemos declarar arrays de cualquier tipo

Tipos primitivos (int,double,char)Como referencias (objetos, interfaces, clases abstractas, arrays) La declaracion de la variable no establece el tama~no Es necesario inicializar el tama~no antes de utilizarlo

En caso contrarioNullPointerExceptionEl rango de elementos de un array es[0..longitud-1]Si accedemos a una posicion negativa o mayor que el tama~no

del array!ArrayIndexOutOfBoundsException

Guillermo Roman, UPM AED: Introduccion 10/42

Ejemplos Arrays

int [ ]a ; a[0] = 4; int [ ]a 2= n ull a[2] = 10; int [ ]b = n ew i nt [20]; b[0] = 7; int [ ]c = n ew i nt [getIntegerFromUser()];

String [] d =

n ew

S tring[10];

d[0] = n ew

S tring("Hola");

int [ ]e = n ew i nt [0]; int [ ]f = { } ; int [ ]g = { 7 ,9 ,8 } ;

Clase [] h =

n ew

S ubClase[5];

Guillermo Roman, UPM AED: Introduccion 11/42

Paso de Par

ametros por Referencia public s tatic v oid s wap( int a rray[]){ int t mp= a rray[0]; array[0] = array[1]; array[1] = tmp; public s tatic v oid m ain(String[ ]a rgs){ int a rray[]= { 3,4}; swap(array);

System.out.println(array[0] +"" + array[1]);

}Pregunta >Que saldra por pantalla?

Guillermo Roman, UPM AED: Introduccion 12/42

Bucles

Buclewhile

INIT while ( COND)

BODYBucledo-while

do BODY while (COND)Buclefor for ( INIT;C OND;P OST) BODY

Guillermo Roman, UPM AED: Introduccion 13/42

Equivalencia Bucles

Equivalenciawhile-do-while

BODY d o while ( COND){ B ODY

BODY }

w hile ( COND)Equivalenciawhile-for INIT for ( INIT;C OND;P OST){ w hile (COND){

BODY BODY

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