Java 错误：表达式的非法开始

Question

我基本上是在提炼、完成和尝试编译 Java 初学者参考书中的测试代码。目标是创建一个猜谜游戏，其中目标位于 3 个连续的单元格中（我将位置保存在一个数组中）并且用户猜测单元格编号。逐个破坏目标细胞。

我在这里查看了六篇关于相同错误的帖子，但我无法弄清楚出了什么问题。

这是我的错误：

test.java:5: error: illegal start of expression
 public int[] locations={1,2,3};
 ^
1 error

我的代码是：

public class test{

        public static void main(String[] args){

            test dot=new test();
            public int[] locations={1,2,3};

            dot.setLocationCells(locations);

            String userGuess="2";
            String result = dot.checkYourself(userGuess);
            String testResult="failed";

            if(result.equals("hit")){
                testResult="passed";
            }


          System.out.println(testResult);
        }

public String checkYourself(String stringGuess){
        int guess=Integer.parseInt(stringGuess);
        String result="miss";
        int numOfHits=0;

        for(int cell:locations){
            if(guess==cell){
                result="hit";
                numOfHits++;
                break;
                }
            }

        if(numOfHits==locations.length){
            result="kill";
            }

       System.out.println(result);
       return result;
    }


public void setLocationCells( int[] locations){
        int[] locns;
        locns=locations;
        }

}

Answer 1

方法只能声明局部变量。这就是为什么当您尝试将其声明为公共时编译器会报告错误的原因。

对于局部变量，您不能使用任何类型的访问器（公共的、受保护的或私有的）。

您还应该知道 static 关键字的含义。在方法checkYourself 中，您使用整数数组locations。

static 关键字区分了可通过对象创建访问的元素。因此它们不是对象本身的一部分。

public class Test { //Capitalized name for classes are used in Java
   private final init[] locations; //key final mean that, is must be assigned before object is constructed and can not be changed later. 

   public Test(int[] locations) {
      this.locations = locations;//To access to class member, when method argument has the same name use `this` key word. 
   }

   public boolean checkYourSelf(int value) { //This method is accessed only from a object.
      for(int location : locations) {
         if(location == value) {
            return true; //When you use key word return insied of loop you exit from it. In this case you exit also from whole method.
         }
      }
      return false; //Method should be simple and perform one task. So you can get more flexibility. 
   }
   public static int[] locations = {1,2,3};//This is static array that is not part of object, but can be used in it. 

   public static void main(String[] args) { //This is declaration of public method that is not part of create object. It can be accessed from every place.
      Test test = new Test(Test.locations); //We declare variable test, and create new instance (object) of class Test.  
      String result;
      if(test.checkYourSelf(2)) {//We moved outside the string
        result = "Hurray";        
      } else {
        result = "Try again"
      }
      System.out.println(result); //We have only one place where write is done. Easy to change in future.
   } 
}

Answer 2

从int[] locations={1,2,3}; 中删除public 关键字。方法内部不允许使用访问修饰符，因为它的可访问性由其方法范围定义。

如果您的目标是在多个方法中使用此引用，您可能希望将声明移到方法之外。

Answer 3

public static int [] locations={1,2,3};

public static test dot=new test();

在main方法上方声明上述变量，代码编译正常。

public static void main(String[] args){

Answer 4

声明

public static int[] locations={1,2,3};

在 main 方法之外。