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Java biblios. principales: java.lang Object String
2023-07-07 18:41:12 -04:00
# 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:
```txt
pe.com.caelum.gargarus
br.com.alura.notas
cl.gov.reg.news
us.com.linode.miapp
```
### Reestructurando proyecto bytebank
Proyecto [bytebank](./bibliotecas/bytebank/src/com/bytebank/)
```txt
📂️ 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](./bibliotecas/bytebank/src/com/bytebank/modelo/Administrador.java)
```java
package com.bytebank.modelo;
public class Administrador extends Funcionario implements Autenticable {
...
```
[TestCuentas](./bibliotecas/bytebank/src/com/bytebank/test/TestCuentas.java)
```java
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
```java
/*
* Bloque Comentario
*/
// Comentario en una linea
```
Javadoc
```java
/**
*
* @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
*/
```
<p align="center">
<img style="align: center;" width="60%" src="./javadoc.png"/>
<br/><br/>
</p>
Clase [Cuenta.java](./bibliotecas/bytebank/src/com/bytebank/modelo/Cuenta.java)
```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](./bibliotecas/bytebank/doc/) en Eclipse en la
barra principal -> *Project* -> *@Generate Javadoc*
### Exportar jar
Se exporta el proyecto anterior:
[bytebank_libreria.jar](./bibliotecas/bytebank_libreria/lib/bytebank_exportado.jar)
Se crea un nuevo proyecto [bytebank_libreria](./bibliotecas/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](./bibliotecas/bytebank_libreria/src/com/bytebank/test/TestLibreria.java)
```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](./bibliotecas/bytebank_libreria/lib/bytebank_ejecutable.jar)
, tiene como punto de entrada
[TestLibreria.java](#creación-de-package-test-y-clase-testlibreria)
> **Note** Revisar la opciones de exportación para incluir o no código fuente
del paquete y/o del JKD.
```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());
}
}
```
Salida
```sh
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](https://mvnrepository.com) central que es público y se puede buscar.
Apache:
[maven](https://maven.apache.org/guides/getting-started/maven-in-five-minutes.html)
in 5 minutes.
<details>
<summary markdown="span"><code>tldr mvn</code></summary>
```txt
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"
```
</details>
<details>
<summary markdown="span"><code>mvn --help</code></summary>
```txt
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
```
</details>
## java.lang
**[java.lang](https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/package-summary.html)**
es la base de lenguaje, sus métodos, objs, etc. Están a disposición sin necesidad
de importarlos. Por ejemplo el
[`String`](https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html)
```java
// String nombre = new String("DevFzn");
// java.lang.String nombre = "DevFzn";
String nombre = "DevFzn";
```
### String
Los Strings son inmutables,
[TestString.java](./bibliotecas/bytebank/src/com/bytebank/test/TestString.java)
```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
<details>
<summary markdown="span">JDK 17</summary>
| 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<String> | 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<String> | 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> 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. |
</details>
</br>
```java
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
```java
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.
```java
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](./bibliotecas/bytebank/src/com/bytebank/test/TestString.java)
```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](./bibliotecas/bytebank/src/com/bytebank/modelo/Cuenta.java)
```java
...
@Override
public String toString() {
return String.format("Cuenta\nNro : %d\nAgnc : %d", this.numero, this.agencia);
}
```
[CuentaAhorro.java](./bibliotecas/bytebank/src/com/bytebank/modelo/CuentaAhorro.java)
```java
...
@Override
public String toString() {
return super.toString();
}
```
Output
```txt
devFzn estudiando con Alura
devFzn estudiando con Alura
3
F
Cuentas creadas: 1
Cuenta
Nro : 22
Agnc : 11
```
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