在主方法中添加代码，调用count类 public class StringDemo4 { public static void main(String[] args) { } public void count(){ int num1=0; int num2=0; int num3=0; // char c='9'; // System.out.println((int)c); byte[] bytes =str.getBytes(); for (byte b:bytes){ if(b>=65&&b<=90){ //A65 Z 90 //a97 z 122 num1++; } else if (b>=97&&b<=122 ) { num2++; } else if (b>=49&&b<=57) { num3++; } } System.out.println(num1); System.out.println(num2); System.out.println(num3); } }

你需要先创建一个StringDemo4的对象，然后通过该对象调用count()方法。代码如下：

public class StringDemo4 {
    public static void main(String[] args) {
        StringDemo4 demo = new StringDemo4();
        demo.count();
    }
    
    public void count(){
        int num1=0;
        int num2=0;
        int num3=0;
        byte[] bytes =str.getBytes();
        for (byte b:bytes){
            if(b>=65&&b<=90){
                num1++;
            } else if (b>=97&&b<=122 ) {
                num2++;
            } else if (b>=49&&b<=57) {
                num3++;
            }
        }
        System.out.println(num1);
        System.out.println(num2);
        System.out.println(num3);
    }
}