java - 错误: int cannot be converted to class?

Question

UnitedStates类是二分查找类

public class UnitedStates
{
// instance variables
private ArrayList <State> states;

public UnitedStates()
{
   states = new ArrayList <State> ();


   readFile();
   printStates();

   searchStates();  
}

public void searchStates()
{
    Scanner keyboard = new Scanner(System.in);
    String ans = "y";
    System.out.println();
    System.out.println("=====================");
    System.out.println("     Searching");
    System.out.println("=====================");

    while(ans.equalsIgnoreCase("y"))
    {
        System.out.println();
        System.out.print("Enter state -->");
        String stateName = keyboard.nextLine();


        State state = binarySearch(states, stateName);

        if(state == null)
           System.out.println("State not found");
        else
        {
          System.out.println();
          System.out.println("State Name       = " + state.getName());
          System.out.println("State Capital    = " + state.getCapital());
          System.out.println("State Nickname   = " + state.getNickname());
          System.out.println("State Population = " + state.getPopulation());
          System.out.println(); 
        }


        System.out.println();
        System.out.print("Search again[Y/N]?");
        ans = keyboard.nextLine();

    }
}

// Performs a binarySearch on states searching for key
// If key is found it returns the State object that
// corresponds to key; otherwise it returns null
public int binarySearch(ArrayList<State> states, String key)
{
        int left = 0;
        int right = states.size() - 1;

        while(left <= right)
        {
            int midpoint = (left + right) / 2;

            int result = states.get(midpoint).compareTo(key);

            if(result == 0)
            {
                return midpoint;
            }
            else if(result < 0)
            {
                left = midpoint + 1;
            }
            else
            {
                right = midpoint - 1;
            }

}
        return -1;
    }

public void printStates()
{
    for(State s : states)
    {
        System.out.printf("%-15s", s.getName());
        System.out.printf("%-15s", s.getCapital());
        System.out.printf("%-25s", s.getNickname());
        System.out.printf("%10s\n", s.getPopulation()); 
    }
}

public void readFile()
{
    Scanner scan = null;
    try
    {
        scan = new Scanner(new File("states.txt"));
    }
    catch(FileNotFoundException ex)
    {
        System.out.println("File not Found!");
    }

    String name;
    String capital;
    String nickname;
    int population;
    while(scan.hasNextLine())
    {
        name = scan.nextLine();
        capital = scan.nextLine();
        nickname = scan.nextLine();
        population = scan.nextInt();
        if(scan.hasNextLine())
        {
          String dummy = scan.nextLine();   
        }


        State state = new State(name, capital, nickname, population);
        states.add(state);
    }



}
}

这是状态类

public class State implements Comparable
{
// instance variables
private String name;
private String capital;
private String nickname;
private int population;

public State(String n, String c, String nn, int p)
{
    name = n;
    capital = c;
    nickname = nn;
    population = p;
}


    public String getName()
{
    return name;
}

public String getCapital()
{
    return capital;
}

public String getNickname()
{
    return nickname;
}

public int getPopulation()
{
    return population;
}

// Comparable Interface method
// Casts obj to a String, then calls the String class's
// compareTo method to compare the name of this state
// to the name passed in the parameter list. It returns
// either a positive number, negative number, or zero.
    @Override
public int compareTo(Object stateName)
{
      State state = (State)stateName;

      String otherStateName = state.getName();

      return name.compareTo(otherStateName);
}

}

我目前正在开发一个二进制搜索项目，并且在解决我确实知道如何解决的错误时遇到问题。我试图在 UnitedStates 类中调用 ("State state = binarySearch(states, stateName);") 行的 binarySearch 方法，但它给出的错误是“不兼容的类型:int 无法转换为 State”。我不知道如何将 int 类型转换为类，如果有人能告诉我如何解决此错误，我将非常感激。

Answer 1

binarySearch 返回一个 int 每

public int binarySearch(ArrayList<State> states, String key)

binarySearch 的注释是错误的。

// If key is found it returns the State object that
// corresponds to key; otherwise it returns null

也许应该是这样

// If key is found it returns the index of the State
// object that corresponds to key; otherwise it returns -1.

您正在尝试将生成的 int 分配给一个状态

State state = binarySearch(...);

也许分配

int stateIndex = binarySearch(...);
State state = null;
if (stateIndex >= 0) {
  state = states.get(stateIndex);
  ...
} else {
  // deal with error.
}