正确使用for循环

Question

在以下代码中,永远不会执行for循环.我试图用断点和手表解决问题.返回密文的正确长度,但for循环直到没有增加int i >= ciphertext.length().事实上,似乎没有任何东西执行过'Debug'消息.

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--){

你需要倒退.还要注意-1,你需要它来避免超出范围的异常(索引开始于0和转到length -1).

当你被困住时,总是用纸和铅笔大声追踪你的循环,这总是有帮助的.