查找 JTextfield 字符串中某些字符的出现次数

Question

I'm pretty new to coding and I'm having trouble with my program. The program I'm trying to run takes the DNA strand that the user provides in a text field (can only include 'A', 'T', 'C', and 'G') and then the program gives you the complementary DNA strand. That part is going well but I then need it to also output the number of times 'A', 'T', 'C', and 'G' occur in the original user's input (*not the complementary strand).

I've found a lot of posts saying that I need to use the code that counts it (I have it in the last code block) but I haven't been able to get it to work with the program and I don't know what I would set the output of each JLabel to be. Sorry this is so long, I just want to provide as much info as possible.

    public void buttonPressed()
{
    String str = input.getText().toUpperCase();
    
    for (int i = 0; i <= str.length(); i++) {
        char letter = str.charAt(i);
    
        if (letter == 'A' || letter == 'T' || letter == 'C' || letter == 'G') {
            
            str = input.getText().toUpperCase();
            str = str.replace("A", "t")
            .replace("T", "a")
            .replace("C", "g")
            .replace("G", "c")
            .toUpperCase();
            compOutput.setText(str);        
            }
        
        else {
            compOutput.setText("Error: input not in DNA format");
            aOut.setText("0");
            cOut.setText("0");
            gOut.setText("0");
            tOut.setText("0");
            return;             
    }                          
  }     
}

/**
 * This is where I'm having trouble, I can't tell if it's even counting
 * the occurrences and if it is, I don't know how to display it in each JLabel.
 * 
 * The JLabels are named aOut, tOut, cOut, gOut
 */

public int countingLetter(String str, char letter) {
    int counter = 0;
    for (int i = 0; i < str.length(); i++) {
        if (str.charAt(i) == letter) {
            counter ++;
        }
    }
    return counter;
    }       
}

Answer 1

Try the following code. I used prints as I don't have JLabels available to print the results. Note that if countingLetter() finds no letter, it will return a 0, so no need for an else statement.

 public void buttonPressed()
{
    //String str = input.getText().toUpperCase();
    String str = "ACTGTCA";
    String originalUserInput = "ACTGTCA";

    for (int i = 0; i <= str.length() - 1; i++) {
        char letter = str.charAt(i);

        if (letter == 'A' || letter == 'T' || letter == 'C' || letter == 'G') {

            str = "ACTGTCA";
            str = str.replace("A", "t")
                    .replace("T", "a")
                    .replace("C", "g")
                    .replace("G", "c")
                    .toUpperCase();
        }
    }
    //compOutput.setText(str);
    System.out.println("Complement: " + str);
    System.out.println("originalUserInput: " + originalUserInput);
    System.out.println("A: " + countingLetter(originalUserInput ,'A'));
    System.out.println("T: " + countingLetter(originalUserInput ,'T'));
    System.out.println("C: " + countingLetter(originalUserInput ,'C'));
    System.out.println("G: " + countingLetter(originalUserInput ,'G'));
    /*
    aOut.setText(countingLetter(originalUserInput ,'A'));
    tOut.setText(countingLetter(originalUserInput ,'T'));
    cOut.setText(countingLetter(originalUserInput ,'C'));
    gOut.setText(countingLetter(originalUserInput ,'G'));

     */
}

/**
 * This is where I'm having trouble, I can't tell if it's even counting
 * the occurrences and if it is, I don't know how to display it in each JLabel.
 *
 * The JLabels are named aOut, tOut, cOut, gOut
 */

public int countingLetter(String str, char letter) {
    int counter = 0;
    for (int i = 0; i < str.length(); i++) {
        if (str.charAt(i) == letter) {
            counter ++;
        }
    }
    return counter;
}

Let me know if it works.