如何使用for循环计算字符串中的空格

Question

我如何编写一个for循环来打印用户输入的字符串中的空格量？在我的for循环中，当我编写if（ch ==“”）时，编译器会说“无法比较的类型：char和java.lang.String”。当我编码（ch ==''）时，它表示“未封闭的字符文字”。提前谢谢

import java.util.Scanner;
public class Count{

public static void main (String[] args){

  Scanner scan = new Scanner (System.in);
  String phrase;    // a string of characters
  int countBlank;   // the number of blanks (spaces) in the phrase 
  int length;       // the length of the phrase
  int i = 0;
  char ch;          // an individual character in the string    
  // Print a program header
  System.out.println ();
  System.out.println ("Character Counter");
  System.out.println ();




  // Read in a string and find its length
  System.out.print ("Enter a sentence or phrase: ");
  phrase = scan.nextLine(); // read input Scanner 
  // Find the length of the phrase 

  // Initialize counts
  countBlank = 0;

  // a for loop to go through the string character by character
  // and count the blank spaces
  for (i = 0; ch < length; i++){
  ch = phrase.charAt(i);
  if (ch == '  ')
  countBlank++;
  }

  // Print the results
  System.out.println ();
  System.out.println ("Number of blank spaces: " + countBlank);
  System.out.println ();
    }
}