java - java中for语句中删除括号与添加括号有什么区别

Question

这个问题已经有答案了:

A single-line loop with a mandatory pair of braces in Java (3 个回答)

已关闭 7 年前。

我在我的项目中尝试了以下代码。

import java.util.*;
public class Test{
    public static void main(String [] args){
        for(int i=0;i<=10;i++)
            Integer k = new Integer(i);//ERROR
        System.out.println("Hello Word");
    }
}

但是，由于这一行，该代码片段无法编译:整数 k = new Integer(i);

和更改自

Integer k = new Integer(i);

至

{Integer k = new Integer(i);}

这个片段没问题

我的问题:

我的代码片段下的 Integer k = new Integer(i); 和 {Integer k = new Integer(i);} 有什么区别？

谢谢

Answer 1

请参阅this answer

每次循环时，您的初始声明都会超出范围，从而使其无用。

方括号创建一个新范围。

范围定义

Scope refers to the lifetime and accessibility of a variable. How large the scope is depends on where a variable is declared. For example, if a variable is declared at the top of a class then it will accessible to all of the class methods. If it’s declared in a method then it can only be used in that method.

Here是范围和范围外的一个很好的例子

// Demonstrate block scope.
class Scope {
  public static void main(String args[])
  {
  int n1; // Visible in main

  n1 = 10;

  if(n1 == 10)
   {
   // start new scope
   int n2 = 20; // visible only to this block

   // num1 and num2 both visible here.
   System.out.println("n1 and n2 : "+ n1 +""+ n2);
   }
   // n2 = 100; // Error! y not known here

   // n1 is still visible here.
    System.out.println("n1 is " + n1);
  }
}