Java之JDK7的新语法探索

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;
 ...
}

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