Oracle_One-Alura_Latam/008_java_oo/bibliotecas_principales.md

Bibliotecas Principales de Java

Programando con Objects y String

• Los packages sirven para organizar nuestro código.

• Los packages son parte del FQN (Full Qualified Name) de la clase.

• El nombre completo de la clase (FQN) consta de: PACKAGE.NOMBRE_SIMPLE_DE_LA_CLASE

• La definición de package debe ser la primera declaración en el código fuente

• Para facilitar el uso de clases de otros packages, podemos importarlas

• Los import son justo después de la declaración del package

• La nomenclatura padrón es usar el nombre de dominio en la web al revés con el nombre del proyecto, por ejemplo:

  pe.com.caelum.gargarus
  br.com.alura.notas
  cl.gov.reg.news
  us.com.linode.miapp
  

Reestructurando proyecto bytebank

Proyecto bytebank

📂️ bibliotecas
└── 📂️ bytebank
    ├── 📁️ bin
    └── 📂️ src
        ├── 📂️ com.bytebank
        │   ├── 📂️ com.bytebank.modelo
        │   │   ├── ☕️ Administrador.java
        │   │   ├── ☕️ Autenticable.java
        │   │   ├── ☕️ AutenticacionUtil.java
        │   │   ├── ☕️ Cliente.java
        │   │   ├── ☕️ Contador.java
        │   │   ├── ☕️ ControlBonificacion.java
        │   │   ├── ☕️ Cuenta.java
        │   │   ├── ☕️ CuentaAhorro.java
        │   │   ├── ☕️ CuentaCorriente.java
        │   │   ├── ☕️ Funcionario.java
        │   │   ├── ☕️ Gerente.java
        │   │   ├── ☕️ SistemaInterno.java
        │   │   ├── ☕️ TestControlBonificacion.java
        │   │   ├── ☕️ TestCuentas.java
        │   │   ├── ☕️ TestFuncionario.java
        │   │   ├── ☕️ TestGerente.java
        │   │   ├── ☕️ TestReferencias.java
        │   │   └── ☕️ TestSistemaInterno.java
        │   └── 📂️ com.bytebank.test
        │       ├── ☕️ TestControlBonificacion.java
        │       ├── ☕️ TestCuentas.java
        │       ├── ☕️ TestFuncionario.java
        │       ├── ☕️ TestGerente.java
        │       ├── ☕️ TestReferencias.java
        │       └── ☕️ TestSistemaInterno.java
        └── 📄️ module-info.java

Imports entre paquetes, Administrador.java

package com.bytebank.modelo;

public class Administrador extends Funcionario implements Autenticable {
    ...

TestCuentas

package com.bytebank.test;
import com.bytebank.modelo.CuentaCorriente;
import com.bytebank.modelo.CuentaAhorro;

public class TestCuentas {
    ...

Modificadores de accesos

Mas a menos restrictivo:

Keyword	Descripción
private	visible solo dentro de la clase
<<package private>>	visible dentro de la clase y dentro del mismo paquete (default)
protected	visible dentro de la clase, del packete y para las cualquier hijo
public	visible desde cualquier paquete

Note

Pueden ser usados en la definición de la clase, atributo, constructor y método.

Javadoc

Comentarios en java

/*
* Bloque Comentario 
*/

// Comentario en una linea

Javadoc

/**
*
* @author (usado en la clase o interfaz)
* @version (usado en la clase o interfaz)
* @param (usado en el método y constructor)
* @return (usado solo en el método)
* @exception o @throws (en el método o constructor)
* @see
* @since
* @serial
* @deprecated
*/

Clase Cuenta.java

    /**
     * Instancia una Cuenta, sin parametros
     */
    public Cuenta() {}

    /**
     * Instancia una Cuenta usando agencia y numero
     * @param agencia
     * @param numero
     */
    public Cuenta(int agencia, int numero) {
        ...

    /**
     * Retira saldo de la cuenta, si no hay saldo suficiente arroja excepción
     * @param valorRetiro
     * @throws SaldoInsuficienteException
    */
    public void retirar(double valorRetiro) throws SaldoInsuficienteException {
        ...

Se puede generar el Javadoc en Eclipse en la barra principal -> Project -> @Generate Javadoc

Exportar jar

Se exporta el proyecto anterior: bytebank_libreria.jar

Se crea un nuevo proyecto bytebank_libreria, donde se crea un directorio lib/ a nivel de src/ y bin/. Luego se agregar el archivo jar en el Build Path, para poder usar sus packetes.

Creación de package test y clase TestLibreria

com.bytebank.test.TestLibreria.java

package com.bytebank.test;

import com.bytebank.modelo.Cuenta;
import com.bytebank.modelo.CuentaCorriente;

public class TestLibreria {
	public static void main(String[] args) {
		Cuenta cuenta = new CuentaCorriente(10, 20);
		cuenta.depositar(500);
		System.out.println(cuenta.getSaldo());
	}
}

Jar Ejecutable

Es un archivo .jar igual al anterior, con la diferencia que este incluye un punto de entrada método main en el archivo MANIFEST.MF, punto donde se inicia el programa.

El ejecutable bytebank_ejecutable.jar , tiene como punto de entrada TestLibreria.java

Note

Revisar la opciones de exportación para incluir o no código fuente del paquete y/o del JDK.

package com.bytebank.test;

import com.bytebank.modelo.Cuenta;
import com.bytebank.modelo.CuentaCorriente;

public class TestLibreria {
	public static void main(String[] args) {
		Cuenta cuenta = new CuentaCorriente(10, 20);
		cuenta.depositar(500);
		System.out.println(cuenta.getSaldo());
	}
}

Salida

java -jar bytebank_ejecutable.jar

Cuentas creadas: 1
500.0

Maven

Java es una plataforma de desarrollo completa que destaca por su gran cantidad de proyectos de código abierto (open source). Para la mayoría de problemas en el día a día del desarrollador ya existen librerías para solucionar. Es decir, si te gustaría conectarte con una base de datos, o trabajar en desarrollo web, en el área de ciencia de datos, creación de servicios o Android, ya existen librerías para esto, muchas veces más de una.

Existe la necesidad de organizar, centralizar y versionar los JARs de esas librerías y administrar las dependencias entre ellos. Para solucionar esto, se crearon herramientas específicas y en el mundo Java se destacó Maven. Maven organiza los JARs (código compilado, código fuente y documentación) en un repositorio central que es público y se puede buscar.

Apache: maven in 5 minutes.

tldr mvn

  mvn

  Apache Maven.
  Tool for building and managing Java-based projects.
  More information: https://maven.apache.org.

  - Compile a project:
    mvn compile

  - Compile and package the compiled code in its distributable format, such as a `jar`:
    mvn package

  - Compile and package, skipping unit tests:
    mvn package -DskipTests

  - Install the built package in local maven repository. (This will invoke the compile and package commands too):
    mvn install

  - Delete build artifacts from the target directory:
    mvn clean

  - Do a clean and then invoke the package phase:
    mvn clean package

  - Clean and then package the code with a given build profile:
    mvn clean -Pprofile package

  - Run a class with a main method:
    mvn exec:java -Dexec.mainClass="com.example.Main" -Dexec.args="arg1 arg2"

mvn --help

usage: mvn [options] [<goal(s)>] [<phase(s)>]

Options:
 -am,--also-make                        If project list is specified, also
                                        build projects required by the
                                        list
 -amd,--also-make-dependents            If project list is specified, also
                                        build projects that depend on
                                        projects on the list
 -B,--batch-mode                        Run in non-interactive (batch)
                                        mode (disables output color)
 -b,--builder <arg>                     The id of the build strategy to
                                        use
 -C,--strict-checksums                  Fail the build if checksums don't
                                        match
 -c,--lax-checksums                     Warn if checksums don't match
    --color <arg>                       Defines the color mode of the
                                        output. Supported are 'auto',
                                        'always', 'never'.
 -cpu,--check-plugin-updates            Ineffective, only kept for
                                        backward compatibility
 -D,--define <arg>                      Define a system property
 -e,--errors                            Produce execution error messages
 -emp,--encrypt-master-password <arg>   Encrypt master security password
 -ep,--encrypt-password <arg>           Encrypt server password
 -f,--file <arg>                        Force the use of an alternate POM
                                        file (or directory with pom.xml)
 -fae,--fail-at-end                     Only fail the build afterwards;
                                        allow all non-impacted builds to
                                        continue
 -ff,--fail-fast                        Stop at first failure in
                                        reactorized builds
 -fn,--fail-never                       NEVER fail the build, regardless
                                        of project result
 -gs,--global-settings <arg>            Alternate path for the global
                                        settings file
 -gt,--global-toolchains <arg>          Alternate path for the global
                                        toolchains file
 -h,--help                              Display help information
 -l,--log-file <arg>                    Log file where all build output
                                        will go (disables output color)
 -llr,--legacy-local-repository         Use Maven 2 Legacy Local
                                        Repository behaviour, ie no use of
                                        _remote.repositories. Can also be
                                        activated by using
                                        -Dmaven.legacyLocalRepo=true
 -N,--non-recursive                     Do not recurse into sub-projects
 -npr,--no-plugin-registry              Ineffective, only kept for
                                        backward compatibility
 -npu,--no-plugin-updates               Ineffective, only kept for
                                        backward compatibility
 -nsu,--no-snapshot-updates             Suppress SNAPSHOT updates
 -ntp,--no-transfer-progress            Do not display transfer progress
                                        when downloading or uploading
 -o,--offline                           Work offline
 -P,--activate-profiles <arg>           Comma-delimited list of profiles
                                        to activate
 -pl,--projects <arg>                   Comma-delimited list of specified
                                        reactor projects to build instead
                                        of all projects. A project can be
                                        specified by [groupId]:artifactId
                                        or by its relative path
 -q,--quiet                             Quiet output - only show errors
 -rf,--resume-from <arg>                Resume reactor from specified
                                        project
 -s,--settings <arg>                    Alternate path for the user
                                        settings file
 -t,--toolchains <arg>                  Alternate path for the user
                                        toolchains file
 -T,--threads <arg>                     Thread count, for instance 2.0C
                                        where C is core multiplied
 -U,--update-snapshots                  Forces a check for missing
                                        releases and updated snapshots on
                                        remote repositories
 -up,--update-plugins                   Ineffective, only kept for
                                        backward compatibility
 -v,--version                           Display version information
 -V,--show-version                      Display version information
                                        WITHOUT stopping build
 -X,--debug                             Produce execution debug output

java.lang

java.lang es la base de lenguaje, sus métodos, objs, etc. Están a disposición sin necesidad de importarlos. Por ejemplo el String

        // String nombre = new String("DevFzn");
        // java.lang.String nombre = "DevFzn";
        String nombre = "DevFzn";

String

Los Strings son inmutables, TestString.java

        String nombre = "DevFzn";

        //nombre.replace = ('D', 'd');
        nombre = nombre.replace('D', 'd');

        //nombre.concat(" estudiando en Alura");
        nombre = nombre.concat(" estudiando con Alura");

Métodos String

JDK 17

Modifier and Type	Method	Description
char	charAt(int index)	Returns the char value at the specified index.
IntStream	chars()	Returns a stream of int zero-extending the char values from this sequence.
int	codePointAt(int index)	Returns the character (Unicode code point) at the specified index.
int	codePointBefore(int index)	Returns the character (Unicode code point) before the specified index.
int	codePointCount(int beginIndex, int endIndex)	Returns the number of Unicode code points in the specified text range of this String.
IntStream	codePoints()	Returns a stream of code point values from this sequence.
int	compareTo(String anotherString)	Compares two strings lexicographically.
int	compareToIgnoreCase(String str)	Compares two strings lexicographically, ignoring case differences.
String	concat(String str)	Concatenates the specified string to the end of this string.
boolean	contains(CharSequence s)	Returns true if and only if this string contains the specified sequence of char values.
boolean	contentEquals(CharSequence cs)	Compares this string to the specified CharSequence.
boolean	contentEquals(StringBuffer sb)	Compares this string to the specified StringBuffer.
static String	copyValueOf(char[] data)	Equivalent to valueOf(char[]).
static String	copyValueOf(char[] data, int offset, int count)	Equivalent to valueOf(char[], int, int).
Optional	describeConstable()	Returns an Optional containing the nominal descriptor for this instance, which is the instance itself.
boolean	endsWith(String suffix)	Tests if this string ends with the specified suffix.
boolean	equals(Object anObject)	Compares this string to the specified object.
boolean	equalsIgnoreCase(String anotherString)	Compares this String to another String, ignoring case considerations.
static String	format(String format, Object... args)	Returns a formatted string using the specified format string and arguments.
static String	format(Locale l, String format, Object... args)	Returns a formatted string using the specified locale, format string, and arguments.
String	formatted(Object... args)	Formats using this string as the format string, and the supplied arguments.
byte[]	getBytes()	Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
void	getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)	Deprecated. This method does not properly convert characters into bytes.
byte[]	getBytes(String charsetName)	Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
byte[]	getBytes(Charset charset)	Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.
void	getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)	Copies characters from this string into the destination character array.
int	hashCode()	Returns a hash code for this string.
String	indent(int n)	Adjusts the indentation of each line of this string based on the value of n, and normalizes line termination characters.
int	indexOf(int ch)	Returns the index within this string of the first occurrence of the specified character.
int	indexOf(int ch, int fromIndex)	Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
int	indexOf(String str)	Returns the index within this string of the first occurrence of the specified substring.
int	indexOf(String str, int fromIndex)	Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
String	intern()	Returns a canonical representation for the string object.
boolean	isBlank()	Returns true if the string is empty or contains only white space codepoints, otherwise false.
boolean	isEmpty()	Returns true if, and only if, length() is 0.
static String	join(CharSequence delimiter, CharSequence... elements)	Returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter.
static String	join(CharSequence delimiter, Iterable<? extends CharSequence> elements)	Returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter.
int	lastIndexOf(int ch)	Returns the index within this string of the last occurrence of the specified character.
int	lastIndexOf(int ch, int fromIndex)	Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
int	lastIndexOf(String str)	Returns the index within this string of the last occurrence of the specified substring.
int	lastIndexOf(String str, int fromIndex)	Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
int	length()	Returns the length of this string.
Stream	lines()	Returns a stream of lines extracted from this string, separated by line terminators.
boolean	matches(String regex)	Tells whether or not this string matches the given regular expression.
int	offsetByCodePoints(int index, int codePointOffset)	Returns the index within this String that is offset from the given index by codePointOffset code points.
boolean	regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)	Tests if two string regions are equal.
boolean	regionMatches(int toffset, String other, int ooffset, int len)	Tests if two string regions are equal.
String	repeat(int count)	Returns a string whose value is the concatenation of this string repeated count times.
String	replace(char oldChar, char newChar)	Returns a string resulting from replacing all occurrences of oldChar in this string with newChar.
String	replace(CharSequence target, CharSequence replacement)	Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
String	replaceAll(String regex, String replacement)	Replaces each substring of this string that matches the given regular expression with the given replacement.
String	replaceFirst(String regex, String replacement)	Replaces the first substring of this string that matches the given regular expression with the given replacement.
String	resolveConstantDesc(MethodHandles.Lookup lookup)	Resolves this instance as a ConstantDesc, the result of which is the instance itself.
String[]	split(String regex)	Splits this string around matches of the given regular expression.
String[]	split(String regex, int limit)	Splits this string around matches of the given regular expression.
boolean	startsWith(String prefix)	Tests if this string starts with the specified prefix.
boolean	startsWith(String prefix, int toffset)	Tests if the substring of this string beginning at the specified index starts with the specified prefix.
String	strip()	Returns a string whose value is this string, with all leading and trailing white space removed.
String	stripIndent()	Returns a string whose value is this string, with incidental white space removed from the beginning and end of every line.
String	stripLeading()	Returns a string whose value is this string, with all leading white space removed.
String	stripTrailing()	Returns a string whose value is this string, with all trailing white space removed.
CharSequence	subSequence(int beginIndex, int endIndex)	Returns a character sequence that is a subsequence of this sequence.
String	substring(int beginIndex)	Returns a string that is a substring of this string.
String	substring(int beginIndex, int endIndex)	Returns a string that is a substring of this string.
char[]	toCharArray()	Converts this string to a new character array.
String	toLowerCase()	Converts all of the characters in this String to lower case using the rules of the default locale.
String	toLowerCase(Locale locale)	Converts all of the characters in this String to lower case using the rules of the given Locale.
String	toString()	This object (which is already a string!)
String	toUpperCase()	Converts all of the characters in this String to upper case using the rules of the default locale.
String	toUpperCase(Locale locale)	Converts all of the characters in this String to upper case using the rules of the given Locale.
R	transform(Function<? super String,? extends R> f)	This method allows the application of a function to this string.
String	translateEscapes()	Returns a string whose value is this string, with escape sequences translated as if in a string literal.
String	trim()	Returns a string whose value is this string, with all leading and trailing space removed, where space is defined as any character whose codepoint is less than or equal to 'U+0020' (the space character).
static String	valueOf(boolean b)	Returns the string representation of the boolean argument.
static String	valueOf(char c)	Returns the string representation of the char argument.
static String	valueOf(char[] data)	Returns the string representation of the char array argument.
static String	valueOf(char[] data, int offset, int count)	Returns the string representation of a specific subarray of the char array argument.
static String	valueOf(double d)	Returns the string representation of the double argument.
static String	valueOf(float f)	Returns the string representation of the float argument.
static String	valueOf(int i)	Returns the string representation of the int argument.
static String	valueOf(long l)	Returns the string representation of the long argument.
static String	valueOf(Object obj)	Returns the string representation of the Object argument.

nombre = nombre.toUpperCase();
System.out.println("Mayúsculas : "+nombre);

nombre = nombre.toLowerCase();
System.out.println("Minúsculas : "+nombre);

int indice = nombre.indexIf('F');
System.out.println("Indice encontrado: "+indice);

char letra = nombre.chartAt(indice);
System.out.println("Caracter en indice(%s) encontrado: %c", indice, letra);

Formato de Strings

Format Specifier	Data Type	Output or Return value
%a	floating point	Returns a Hex output of floating point number
%b	Any type	True or False
%c	character	Unicode character
%d	integer	Decimal Integer
%e	floating point	a decimal number in scientific notation
%f	floating point	decimal number
%g	floating point	decimal number, possibly in scientific notation depending on the precision and value
%h	Any type	Hex String of value from hashCode() method
%n	None	Platform-specific line separator
%o	integer	Octal number
%s	Any type	String value
%t	Date/Time	%t is the prefix for Date/Time conversions
%x	integer	Hex string

StringBuilder

        String texto = "Ayuda";
        texto = texto.concat("-");
        texto = texto.concat("me ");
        texto = texto.concat("subí ");
        texto = texto.concat("al ");
        texto = texto.concat("bus ");
        texto = texto.concat("equivocado ");
        System.out.println(texto);

Esto no es bueno pensando en el rendimiento. Para esto existe la clase StringBuilder que ayuda a concatenar Strings de manera más eficiente.

        StringBuilder builder = new StringBuilder("Ayuda");
        builder.append("-");
        builder.append("me ");
        builder.append("subí ");
        builder.append("al ");
        builder.append("bus ");
        builder.append("equivocado ");
        String texto = builder.toString();
        System.out.println(texto);

StringBuilder es una clase común. Se utiliza new para crear el objeto, mutable, (usa la misma referencia, sin nuevas asignaciones). E implementa la interfaz CharSequence. Es decir, algunos métodos de la clase String con comunes con StringBuilder.

System

Note

Métodos staticos son accesibles sin requerir una instancia

Object

Clase principal de java, todos los objetos heredan de Object

TestString.java

package com.bytebank.test;

import com.bytebank.modelo.CuentaAhorro;

public class TestString {
    public static void main(String[] args) {
        String nombre = "DevFzn";
        nombre = nombre.replace('D', 'd');
        nombre = nombre.concat(" estudiando con Alura");
        System.out.println(nombre);

        printLine(nombre);
        printLine(nombre.indexOf("F"));
        printLine(nombre.charAt(3));
        printLine(new CuentaAhorro(11, 22));
}

    public static void printLine(Object valor) {
        System.out.println(valor.toString());
    }
    // Sobrecargando método printLine()
    public static void printLine(String msj) {
        System.out.println(msj);
    }
    public static void printLine(int valor) {
        System.out.println(valor);
    }
    public static void printLine(char caracter) {
        System.out.println(caracter);
    }
}

Cuenta.java

    ...
    @Override
    public String toString() {
        return String.format("Cuenta\nNro  : %d\nAgnc : %d", this.numero, this.agencia);
    }

CuentaAhorro.java

    ...
    @Override
    public String toString() {
        return super.toString();
    }

Output

devFzn estudiando con Alura
devFzn estudiando con Alura
3
F
Cuentas creadas: 1
Cuenta
Nro  : 22
Agnc : 11