java - 错误地使用for循环

Question

在下面的代码中，for 循环永远不会被执行。我尝试通过断点和监视来解决问题。返回密文的正确长度，但是 for 循环直到 int i >= ciphertext.length() 才会递增。事实上，除了“调试”消息之外，似乎没有任何内容执行。

private void decrypt_btnActionPerformed(java.awt.event.ActionEvent evt) {                                            


    String alphabet= "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    String ciphertext="fRcXFBxXTRJ";


    status_label.setText( "Decryption has begun" );

    JOptionPane.showMessageDialog(null,"ciphertext-length: " + ciphertext.length() + "\n" + ciphertext,"Debug", JOptionPane.INFORMATION_MESSAGE);

    for (int i = 0; i>=ciphertext.length(); i--){

        System.out.println("inc:" + i);

        String cipher_current_char = getLetterAtIndex(ciphertext, i);
        int pos_char_in_alphabet = getIndexAtLetter(alphabet, cipher_current_char);


        if(pos_char_in_alphabet-2<0){

            plain_ta.setText(getLetterAtIndex(alphabet, (alphabet.length()+(pos_char_in_alphabet -2)+1 ) ));

            status_label.setText( 100/i + "%");



        }else{

            cipher_current_char = getLetterAtIndex(ciphertext, i);

            pos_char_in_alphabet = getIndexAtLetter(alphabet, cipher_current_char);

            plain_ta.setText(getLetterAtIndex(alphabet, (pos_char_in_alphabet-2)));

            status_label.setText( 100/i + "%");

        }
    }
}                          

Answer 1

for (int i = ciphertext.length()-1; i>=0; i--){

你需要逆向工作。另请注意 -1，您需要它来避免越界异常(索引从 0 开始并转到 length -1 )。

当你遇到困难时，总是用纸和铅笔大声地描绘出你的循环，这总是有帮助的。