java - 通过使用while/for循环，如何仅减去用户输入的一行的大写字母？

Question

这是我的代码，我使用 is.upperCase 进行检查，但它似乎不起作用。我很难将所有大写字母连接在一起。任何建议和帮助将不胜感激!

import java.util.Scanner;

public class UpperCase  {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in); 
        System.out.print("Please input a random line that contain uppercase letters in any positions: ");
        String str = in.next();

        int i = 0;

        while (i < str.length() - 1) {
            if(Character.isUpperCase(i)) { 
                char upperLetter = str.charAt(i);
            }    

            Object outputLetter = str.charAt(0) + str.charAt(i++);
            char upperLetter = str.charAt(i++);
        }

        System.out.println("The uppercase letters are:" );
    }
}

Answer 1

我想下面的内容可以解决您的问题。

        Scanner in = new Scanner(System.in);
        System.out.print("Please input a random line that contain uppercase letters in any positions: ");
        String str = in.nextLine();
        char[] cr = str.toCharArray();
        StringBuffer stringBuffer = new StringBuffer();
        for(int i=0;i<cr.length;i++){
            if(Character.isUpperCase(cr[i])){
                stringBuffer.append(cr[i]);
            }
        }
        System.out.println("The uppercase letters are:" + stringBuffer);