JavaPHP

老板要求的Java和PHP类比学习

一、java是什么

Java编程语言是一种高级语言，可以通过以下所有流行语来表征，同时相比PHP，使用❎⛔️✅：

• Simple【简单】❎
• Object oriented【面向对象】⛔️
• Distributed 【分布式】✅
• Multithreaded【多线程】✅
• Dynamic【动态】❎
• Architecture neutral【架构中立性】✅
• Portable【可移植】⛔️
• High performance【高性能】✅
• Robust【强壮】✅
• Secure【安全】✅

java编译过程：.java ->.class->01100，编译器是JavaVM

php编译过程：.php->opcode->01100，编译器是ZendVM

二、安装

1、Mac

// java
brew install java
// php
brew install php

2、包管理

// java maven
brew install maven
// php composer
brew install composer

三、你好，世界

// HelloWorldApp.java
class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}
javac HelloWorldApp.java
java HelloWorldApp

// HelloWorldApp.php
<?php
    echo "Hello World!";
php HelloWorldApp.php

四、面向对象概述

楼主说：php的面向对象与java的面向对象基本一致，原因是php借鉴java

对象object：类似现实世界的对象，他们都拥有状态和关系行为。一个对象存储他们的状态在一个变量和暴露他们的行为通过方法

封装encapsulation：隐藏状态并通过方法进行交互

类class：我们经常会讲到new一个对象，解读为对象是类的实例，类是对象的蓝图

继承inherit：继承来自父类的状态和方法

接口interface：制定一套规范方法给类使用

包package：命名空间，类似电脑中的文件夹

五、语言基础

楼主说：java和php基本一致，只是java是强类型语言，需要定义变量的类型

1、变量

变量种类

• 实例变量⛔️
• 静态变量✅
• 常量⛔️
• 参数⛔️

主要数据类型

// java
float pi = 3.14;
// php
$pi = 3.14;

• byte
• short
• int
• long
• float
• double
• boolean
• char

数组

// java
int[] arr = {1,2,3};
int[][] array = {
    {1,2,3},
    {4,5,6},
    {7,8,9}
};
// php
$arr = [1,2,3];
$array = [
    [1,2,3],
    [4,5,6],
    [7,8,9]
];

###2、运算符

java和php⛔️

###3、表达式

java和php⛔️

4、流程控制

java和php⛔️

六、类与对象

1、类概述

public class Bicycle {

    // 预定义变量
    public int cadence;
    public int gear;
    public int speed;

    // 构造函数
    public Bicycle(int startCadence, int startSpeed, int startGear) {
        gear = startGear;
        cadence = startCadence;
        speed = startSpeed;
    }

    // 设置踏板
    public void setCadence(int newValue) {
        cadence = newValue;
    }

    // 设置齿轮
    public void setGear(int newValue) {
        gear = newValue;
    }

    // 减速
    public void applyBrake(int decrement) {
        speed -= decrement;
    }

    // 加速
    public void speedUp(int increment) {
        speed += increment;
    }
}

public class MountainBike extends Bicycle {

    public int seatHeight;

    public MountainBike(int startHeight, int startCadence, int startSpeed, int startGear){
        super(startCadence, startSpeed, startGear);
        seatHeight = startHeight;
    }

    public void setHeight(int newValue) {
        seatHeight = newValue;
    }

}

<?php
class Bicycle
{
    // 预定义变量
    public $cadence;
    public $speed;
    public $gear;

	// 构造函数
    public function __construct(int $startCadence, int $startSpeed, int $startGear)
    {
        $this->cadence = $startCadence;
        $this->speed = $startSpeed;
        $this->gear = $startGear;
    }

    // 设置踏板
    public function setCadence(int $newValue)
    {
        $this->cadence = $newValue;
    }

    // 设置齿轮
    public function setGear(int $newValue)
    {
        $this->gear = $newValue;
    }

    // 减速
    public function applyBrake(int $decrement)
    {
        $this->speed -= $decrement;
    }

    // 加速
    public function speedUp(int $increment)
    {
        $this->speed += $increment;
    }
}

<?php
class MountainBike extends Bicycle
{
    public $seatHeight;

    public function __construct(int $startHeight, int $startCadence, int $startSpeed, int $startGear)
    {
        parent::__construct($startCadence, $startSpeed, $startGear);
        $this->seatHeight = $startHeight;
    }


    public function setHeight(int $newValue)
    {
        $this->seatHeight = $newValue;
    }
}

2、对象

public static void main(String[] args) {
    // 实例化对象
    Bicycle myBike = new Bicycle(30, 0, 8);

    System.out.println(myBike.cadence+" "+myBike.gear+" "+myBike.speed);
}

// 实例化对象
$bicycle = new Bicycle(30, 0, 8);

echo $bicycle->cadence." ".$bicycle->speed." ".$bicycle->gear."\n";

3、类进阶

✅

// java可以有多个构造函数，根据参数不同而生成的对象不同
public class Rectangle {
    private int x, y;
    private int width, height;
        
    public Rectangle() {
        this(0, 0, 1, 1);
    }
    public Rectangle(int width, int height) {
        this(0, 0, width, height);
    }
    public Rectangle(int x, int y, int width, int height) {
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;
    }
    
}

4、类嵌套

✅

public class ShadowTest {

    public int x = 0;

    class FirstLevel {

        public int x = 1;

        void methodInFirstLevel(int x) {
            System.out.println("x = " + x);
            System.out.println("this.x = " + this.x);
            System.out.println("ShadowTest.this.x = " + ShadowTest.this.x);
        }
    }

    public static void main(String... args) {
        ShadowTest st = new ShadowTest();
        ShadowTest.FirstLevel fl = st.new FirstLevel();
        fl.methodInFirstLevel(23);
    }
}
x = 23
this.x = 1
ShadowTest.this.x = 0

5、枚举

✅

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
    THURSDAY, FRIDAY, SATURDAY 
}

七、注解

✅

1、替代注释

public class Generation3List extends Generation2List {

   // Author: John Doe
   // Date: 3/17/2002
   // Current revision: 6
   // Last modified: 4/12/2004
   // By: Jane Doe
   // Reviewers: Alice, Bill, Cindy

   // class code goes here
}

@interface ClassPreamble {
   String author();
   String date();
   int currentRevision() default 1;
   String lastModified() default "N/A";
   String lastModifiedBy() default "N/A";
   // Note use of array
   String[] reviewers();
}

@ClassPreamble (
   author = "John Doe",
   date = "3/17/2002",
   currentRevision = 6,
   lastModified = "4/12/2004",
   lastModifiedBy = "Jane Doe",
   // Note array notation
   reviewers = {"Alice", "Bob", "Cindy"}
)
public class Generation3List extends Generation2List {

// class code goes here

}

2、预定义注解

• @Deprecated
• @Override
• @SuppressWarnings
• @SafeVarargs
• @FunctionalInterface
• @Retention
• @Documented
• @Target
• @Inherited
• @Repeatable

八、接口和继承

1、接口

✅

// java
// 接口继承接口
public interface GroupedInterface extends Interface1, Interface2, Interface3 {
    // code
}
// 实现接口
public class RectanglePlus implements Relatable {
    // code
}

// php
interface GroupedInterface
{
    // code
}
class RectanglePlus implements Relatable
{
    // code
}

2、继承

⛔️

// java
public class Bicycle {
    // code
}
public class MountainBike extends Bicycle {
    // code
}
public class Pegasus extends Horse implements Flyer, Mythical {
    // code
}

// php
class Bicycle {
    // code
}
class MountainBike extends Bicycle {
    // code
}
class Pegasus extends Horse implements Flyer, Mythical {
    // code
}

3、多态

✅

public class MountainBike extends Bicycle {
    // 通过重载实现多态
    public void printDescription() {
        super.printDescription();
        System.out.println("The " + "MountainBike has a" +
            getSuspension() + " suspension.");
    }
}

4、对象作为超类

✅

• protected Object clone() throws CloneNotSupportedException

• public boolean equals(Object obj)

• protected void finalize() throws Throwable

• public int hashCode()

• public String toString()

5、抽象方法

⛔️

public abstract class GraphicObject {
   abstract void draw();
}

abstract class GraphicObject {
   abstract function draw();
}

九、数字和字符串

Java是纯面向对象语言，所有都是类，一些数字和字符串操作都得使用类，而PHP中是函数❎

1、数字类

Class Number

2、字符类

Class Character

3、字符串类

Class String

4、装箱和拆箱

todo

十、泛型

✅

1、为什么使用泛型

// 普通写法 需要强制转换
List list = new ArrayList();
list.add("hello");
String s = (String) list.get(0);

// 泛型写法 不需要强制转换
List<String> list = new ArrayList<String>();
list.add("hello");
String s = list.get(0);

2、泛型类型

通常使用的类型变量名字：

• E - Element (used extensively by the Java Collections Framework)
• K - Key
• N - Number
• T - Type
• V - Value
• S,U,V etc. - 2nd, 3rd, 4th types

十一、异常处理

⛔️

public class ListOfNumbers {

    private List<Integer> list;
    public static final int SIZE = 10;

    public ListOfNumbers() {
        list = new ArrayList<Integer>(SIZE);
        for (int i = 0; i < SIZE; i++) {
            list.add(new Integer(i));
        }
    }

    public void writeList(){
        PrintWriter out = null;
        try {
            System.out.println("Entered try statement");
            out = new PrintWriter(new FileWriter("src/HelloWorldApp/OutFile.txt"));

            for (int i = 0; i < SIZE; i++) {
                out.println("Value at: " + i + " = " + list.get(i));
            }
        } catch (IndexOutOfBoundsException e) {
            System.err.println("IndexOutOfBoundsException: " + e.getMessage());
        } catch (IOException e) {
            System.err.println("Caught IOException: " + e.getMessage());
        } finally {
            if (out != null) {
                System.out.println("Closing PrintWriter");
                out.close();
            } else {
                System.out.println("PrintWriter not open");
            }
        }
    }

    public static void main(String[] args) {
        ListOfNumbers numbers = new ListOfNumbers();
        numbers.writeList();
    }
}

十二、基本输入输出

⛔️

public class CopyBytes {
    public static void main(String[] args) throws IOException {
        FileInputStream in = null;
        FileOutputStream out = null;

        try {
            in = new FileInputStream("src/HelloWorldApp/xanadu.txt");
            out = new FileOutputStream("src/HelloWorldApp/outagain.txt");

            int c;
            while ((c = in.read()) != -1) {
                out.write(c);
            }
        } finally {
            if (in != null) {
                in.close();
            }
            if (out != null) {
                out.close();
            }
        }
    }
}

十三、并发

✅

1、线程对象

// 方法1
public class HelloRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Hello from a thread!");
    }

    public static void main(String[] args) {
        (new Thread(new HelloRunnable())).start();
    }
}
// 方法2
public class HelloThread extends Thread {

    @Override
    public void run() {
        System.out.println("Hello from a thread!");
    }

    public static void main(String[] args) {
        (new HelloThread()).start();
    }
}