JAVA技巧:關(guān)于java產(chǎn)生隨機(jī)數(shù)代碼

for(int i=0; readomNumStart.length()<4; i++) {
    if(difficult == 1) {
    //產(chǎn)生隨機(jī)的0-9的數(shù)字
    a = String.valueOf((int)(Math.random() * 10)) ;
    }
    if(difficult == 2) {
    //在0-9和a，b，c，d中隨機(jī)產(chǎn)生。
    String[] readomWord = {"0","1","2","3","4","5","6","7","8","9","a","b","c","d"};
    int readomWordIndex = (int)(Math.random() * 13);
    a = readomWord[readomWordIndex];
    }
    if(difficult == 3) {
    //產(chǎn)生隨機(jī)的字母
    char readomLetter = (char)(Math.random ()*26+’a’);
    a = String.valueOf(readomLetter) ;
    }
    if(difficult == 4) {
    //產(chǎn)生隨機(jī)的數(shù)字和字母的組合
    String[] readomHard = new String[20];
    int readomWordIndex = (int)(Math.random() * 19);
    for(int j=0; j<20; j++) {
    int readomWordNum = (int)(Math.random() * 10);
    char readomLetter = (char)(Math.random ()*26+’a’);
    if(readomWordNum % 2 == 0) {
    readomHard[j] = readomWordNum + "";
    }else{
    readomHard[j] = String.valueOf(readomLetter);
    }
    }
    a = readomHard[readomWordIndex];
    }
    //這樣寫代碼比較短。我也參考了許多人的代碼大部分都很復(fù)雜。我不喜歡寫那么多代碼，所以就這樣寫了。還不能知道這樣寫效率有沒有問題，在我本機(jī)上運(yùn)行沒有什么感覺