为什么在调用排序方法时会出现此异常？

Exception in thread "JavaFX Application Thread"
java.lang.IllegalArgumentException: 1 > 0

jdk:1.8.0 u281
这是学校的作业。我绝对必须递归地解决这个问题，因为它需要使用字母顺序的递归排序方法。

public void sort1() {
    ArrayList<String> sortlist = new ArrayList();

    for(int i = 0; i < size(); i ++) {
        sortlist.add(getInd(i));
    }
    String[] testData = sortlist.toArray(new String[sortlist.size()]);
    sort(testData);
    for(String s: testData) {
        System.out.println(s);
    }
}

/**
 * recursive alphabetical sort method
 * @param a the array of string values
 */
public void sort(String[] a) {  
    if (a.length==1) {
        System.out.println("list is not long enough");
    }
    // Copy array from 1..length-1 into new array rest
    String rest [] = Arrays.copyOfRange(a, 1, a.length);
    // sort rest
    sort(rest);
    // insert a[0] into rest and store the result in a
    insert(a,rest);
}

// insert a[0] into sort and store result in a
private static void insert(String [] a, String [] sorted) {
    int i;
    String saveFirst = a[0];

    // Find index 'i' where such that sorted[i] > a[0]
    for (i=0; i < sorted.length; i++) {
        if (saveFirst.compareTo(sorted[i])<0) {
            break;
        }
    }
    // Copy elements less than a[0] from sorted to a
    for (int j=0; j < i; j++) {
        a[j] = sorted[j];
    }
    // insert a[0]
    a[i] = saveFirst;
    // copy elements greater than a[0] from sorted to a

    for (int j=i+1; j < a.length; j++) {
        a[j] = sorted[j-1];
    }
}

同样的异常也出现在单独类的事件处理程序和开关中：

@Override
public void handle(ActionEvent event)
{
    // Get the command from the command textfield.
    TextField cmdTextField = (TextField)event.getTarget();
    String cmdText =  cmdTextField.getText();

    // Use a scanner to read the name of the linked list  
    // method and do a switch on it.
    Scanner sc = new Scanner(cmdText);
    String cmd = sc.next();
    switch(cmd)
    {
        case "sort":
            ll.sort1();
            break;
    }
}