Java之JDK7的新语法探索

Dear 丶 2021-09-17 09:50 351阅读 0赞

![标题图][20181221114042678]

> `Java`之`JDK7`的新语法探索

## 前言 ##

感谢! 承蒙关照~

字面量:

各种精致的表达方式:

八进制以`0`开头,十六进制`0X`开头,二进制以`0B`开头.

二进制运算时,应该写成这样才直观:

&15 -> &0B1111

`JDK7`使用下划线`(_)`对数据进行分隔.

下划线不要这样做:

不要用于进制标识和数值之间,不要定义在数值开头和结尾,不要定义在小数点旁边.

// 错误
    0B_1111; _0X32_;  1_._223;

二进制的表示方式:

public class BinaryDemo {
     public static void main(String[] args){
      // 定义二进制0B开头
      int x=0B111100;
      System.out.println(x);
      int n1 = x & 0b1111;
      System.out.println(n1);
      // 用下划线
     int y = 12_34_56;
     int z = 0b111_0123_234;
     double b = 23.223_23;
     }
    }

> `switch`

public class Demo{
     public static void main(String[] args){
      int week = 1;
      // 会在内存中进行存储,运算中的数值存储起来运算
      if(week == 1){
       System.out.println("星期一");
      }else if(week == 2){ 
       System.out.println("星期二");
      }else {
       System.out.println("输入错误");
      }
     }
     // 字节码,标记,选择的值,是一个标识,对应的执行的代码
     switch(week){
      case 1:
       System.out.println("星期一");
       break;
      case 2:
       System.out.println("星期二");
       break;
      default:
       System.out.println("输入错误");
     }
     
      public static void Demo(){
       String sex="男";
       if(sex.equals("男")){ 
        System.out.println("男");
       }else{
        System.out.println("女");
       }
       // 编译器的强大
       switch(sex){
        case "男":
         System.out.println("你好");
         break;
        case "女":
         System.out.println("你好");
         break;
        default:
         System.out.println("hello");
       }
      }
    
    }

// sex.hashCode();
    {
     String sex = "男";
     String s;
      switch ((s=sex).hashCode())
      {
       default:
        break;
       case 22899:
        if(!s.equals("女"))
         break;
        System.out.println("女孩你好"); 
        break labe10;
       case 30007:
        if(s.equals("男"))
        {
          System.out.println("先生");
          break labe10;
        }
        break;
      }
      System.out.println("你好");
    }

> 泛型

`Java7`简化,左边定义类型,右边不用定义类型,写`<>`;

for(Iterator<String> it = list.iterator(); it.hasNext(); ){
     System.out.pritnln(it.next());
    }

List<String> list = new ArrayList<>();

public class Demo {
     public static void main(String[] args){
      // List<String> list = new ArrayList<String>();
      List<String> list = new ArrayList<>();
      list.add("abc");
      // Iterator<String> it = list.iterator();
      
     }
    }

> `catch`

public class Demo{
     int[] arr=new int[3];
     try{
      int element = getElement(arr,1);
     }catch(throwNullPointerException){
    
     }catch(ArrayIndexOutOfBoundsException){
    
     }
    
     try{
      int element = getElement(arr,1);
     }catch(throwNullPointerException || ArrayIndexOutOfBoundsException e){
    
     }
    }
    // 添加数组,添加角标元素
    public static int getElement(int[] arr, int index) throws NullPointerException, ArrayIndexOutOfBoundsException{
     if(arr == null){
      throw new NullPointerException("数组不存在");
     }
     if(index<0 || index>= arr.length){
      throw new ArrayIndexOutOfBoundsException("数组角标不存在'');
     }
     return arr[index];
    }

## `try_with_resource` ##

public class Demo{
     public static void main(String[] args){
      FileReader fr = null;
      try{
       fr = new FileReader ("dashu.txt");
       int ch = fr.read();
       System.out.println(ch);
       }catch(IOException e){
       
       }finally{
          fr.close();
       }
     }
    }

声明:

public static void function() throws IOException{
     FileReader fr = null;
     try{
      fr = new FileReader("dashu.txt");
      int ch = fr.read();
      System.out.println(ch);
      }finally{
       if(fr!=null)
        try{
         fr.close();
        }catch(IOException e){
         throw new RuntimeException();
        }
      }
     }
    }

// 自动释放,关闭的资源会在try()中定义
    public static void Demo() throws IOException{
     try(FileReader fr = new FileReader("dashu.txt");FileWriter fw = new FileWriter("dashucoding.txt")) {
      int ch = fr.read();
      fw.write(ch);
      System.out.println(ch);
     }
    }

public static void function() throws IOException{
     Exception exception;
     exception = null;
     Object obj = null;
     FileReader fr = new FileReader("dashu.txt");
     FileWriter fw = new FileWriter("dashucoding.txt");
     int ch = fr.read(); 
     fw.write(ch);
     System.out.println(ch); 
     if(fw != null)
       fw.close();
     break MISSING_BLOCK_LABFL_66;
     exception;
     ...
    }

> 达叔小生：往后余生，唯独有你  
> You and me, we are family !  
> 90后帅气小伙，良好的开发习惯；独立思考的能力；主动并且善于沟通  
> 简书博客： 达叔小生  
> [https://www.jianshu.com/u/c785ece603d1][https_www.jianshu.com_u_c785ece603d1]

## 结语 ##

*  下面我将继续对 其他知识 深入讲解 ，有兴趣可以继续关注
 *  小礼物走一走 or 点赞

[20181221114042678]: /images/20210724/6cc87634d90a44d79480d7a387cd79e2.png
[https_www.jianshu.com_u_c785ece603d1]: https://www.jianshu.com/u/c785ece603d1