UdaCity学习Java记录（3）通用类型

January 19, 2022

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##Exceptions
处理异常及错误。
###举例，电话类
```Java
public class Phone {
    private String phoneType;
    private String phoneNumber;

public Phone(String phoneType, String phoneNumber) {
        if (phoneType == null || phoneNumber == null) {
            throw new IllegalArgumentException("The phone number or type can't be null");
        }
        this.phoneType = phoneType;
        this.phoneNumber = phoneNumber;
    }

public String getPhoneType(){
        return phoneType;
    }

public void setPhoneType(String phoneType){
        this.phoneType=phoneType;
    }

public String getPhoneNumber(){
        return phoneNumber;
    }

public void setPhoneNumber(String phoneNumber){
        this.phoneNumber=phoneNumber;
    }

@Override
    public String toString(){
        return "Phone number: "+phoneNumber+" Phone type: "+phoneType;
    }
}
```
###异常实例举例
```Java
public class PhoneExceptionTester {

public static void main(String[] args) {
        String[] types = new String[]{"Blackberry", "iPhone", "HuaWei", null};
        String[] numbers = new String[]{"123-4567-78", "456-7899-98", null, "852-456-966"};
        for (String i : types
        ) {
            for (String k : numbers
            ) {
                try {
                    System.out.println(new Phone(i, k));
                } catch (IllegalArgumentException e) {
                    System.out.println(e.getLocalizedMessage());
                }
            }
        }
    }
}
```
##Enums
枚举固定变量。
###举例，红绿灯类
```Java
public class Light {
    public Light() {
    }

public void changeColor(LightColor currentLight) {
        if (currentLight==LightColor.RED) {
            System.out.println("Hey! Stop! Put Your hands on the air!");
        } else if (currentLight==LightColor.GREEN) {
            System.out.println("Go away!");
        } else if (currentLight==LightColor.YELLOW) {
            System.out.println("Hey! Slow down! Take it easy.");
        }
    }
}
```
###实现一个灯光颜色的具体对象类
```Java
public class LightChanger {

public static void main(String[] args) {
        Light hld=new Light();
        hld.changeColor(LightColor.YELLOW);
        hld.changeColor(LightColor.RED);
        hld.changeColor(LightColor.GREEN);
    }
}
```
###枚举
```Java
public enum LightColor {
    RED,YELLOW,GREEN;
}
```
####还可以有另一种写法
以房间类型选择为例，返回枚举的类型列表
```Java
public enum RoomType {
    SINGLE("1"), TWIN("2"), DOUBLE("3"), TRIPLE("4"), SUITE("5"), VILLA("6");
    public final String typeLabel;

private RoomType(String typeLabel) {
        this.typeLabel = typeLabel;
    }

public static RoomType valueOfType(String typeLabel) {
        for (RoomType roomType : RoomType.values()) {
            if (roomType.typeLabel.equals(typeLabel)) {
                return roomType;
            }
        }
        throw new IllegalArgumentException();
    }
}
```
##Dates 和 Calendar
存储和检索日期。
```Java
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DatesAndCalendar {

public static void main(String[] args) {
        DatesAndCalendar.displayCurrentDate();
        DatesAndCalendar.displaySetDate();
    }

private static void displayCurrentDate() {
        Calendar calendar = Calendar.getInstance();
        System.out.println(calendar);
        Date date = new Date();
        calendar.setTime(date);
        System.out.println(calendar.getTime());
    }

private static void displaySetDate() {
        Calendar calendar = Calendar.getInstance();
        calendar.set(2189, 2, 27);
        Date date = calendar.getTime();
//        System.out.println(date);
        SimpleDateFormat timeFormat = new SimpleDateFormat("yyyy-MM-dd Sat Jan");
        System.out.println(timeFormat.format(date));
    }

}
```
##Regular Expressions (RegEx)
正则表达式(RegEx)，查找字符串模式。
###举例，person类
```Java
import java.util.regex.Pattern;

public class Person {
    private final String name;
    private final String email;

public Person(String name, String email) {
        this.name = name;
        this.email = email;
        String emailRegex = "^(.+)@(.+).[a-z]";
        Pattern pattern = Pattern.compile(emailRegex);
        if (!pattern.matcher(email).matches()) {
            throw new IllegalArgumentException("Error, Invalid email");
        }
    }

@Override
    public String toString() {
        return "Person{" +
                "Name='" + name + '\'' + ", Email='" + email + '\'' + "}";
    }
}
```
###测试实例
```Java
public class RegExTest {
    public static void main(String[] args) {
        String[] email = new String[]{"ciel@gmail.com", "@gmail.com", "jeff@example.com","asdguh@asdf.com"};
        Person anyone = new Person("Ciel", email[3]);
        System.out.println(anyone.toString());
    }
}
```
##高级字符串特性
更有效地操作和处理字符串。

###Scanner类
```Java
import java.util.Scanner;

public class UserInputTester {

public static void main(String[] args) {
        Scanner sc =new Scanner(System.in);
        try {
            System.out.println("Enter a String:");
            String str=sc.nextLine();
            System.out.println("Your input string is: "+str);
        }catch (Exception ex){
            ex.getLocalizedMessage();
        }finally {
            sc.close();
        }
    }
}
```
###String类基础
```Java
public class StringFunction {
    public static void main(String[] args) {
        String str = "Keep going,Do not give up!";
        System.out.println(str);
        String anotherStr = "Keep going,Do not give up!";
        System.out.println(anotherStr);
        str = "absolutely";
        System.out.println(str);

System.out.println("charAt: " + anotherStr.charAt(5));
        System.out.println("equalsIgnoreCase: " + anotherStr.equalsIgnoreCase("keep going,do not give up!"));
        System.out.println("replace: " + anotherStr.replace("going", "goaaaing"));
        String[] temp = anotherStr.split(" ");
        for (String tempStr : temp
        ) {
            System.out.println("anotherStr.split(\" \"): " + tempStr);
        }
        System.out.println("substring: " + anotherStr.substring(2, 5));
        System.out.println("contains: " + anotherStr.contains("not"));
    }
}
```

UdaCity学习Java记录（3）通用类型