产生60个随机数并代表学生的成绩，并在每个成绩后输出优良中合格不合格，

按照你的改了一下下

public static void main(String[] args) {
         
        int k=0;
        int a[] =new int[60];
        for(int score=0;score<60;score++) {
            if(score%10==0) {
                System.out.println();
            }
            a[score] = (int)(50*Math.random()+50);
            System.out.print(a[score]+"-"+printGrade(a[score])+" ");        
        }
        
    }
    
    private static String printGrade(int  score){
        String flag="";
            if(score>=90) {
                flag="优";
            }else if(score>=80) {
                flag="良";
            }else if(score>=80) {
                flag="中";
            }else if(score>=80) {
                flag="合格";
            }else {
                flag="不合格";
            }
        return flag;
    }

List<Integer> collect2 = ThreadLocalRandom.current().ints(10, 100).limit(60).boxed().collect(Collectors.toList());
        int a = 0;
        for (Integer integer : collect2) {
            if (a % 10 == 0){
                System.out.println();
            }
            String str = "";
            if (integer >= 90){
                str = "优  秀";
            }else if (integer >= 80){
                str = "良  好";
            }else if (integer >= 70){
                str = "中  等";
            }else if (integer >= 60){
                str = "合  格";
            }else {
                str = "不合格";
            }
            System.out.print(integer + " " + str + "  ");

            a ++;
        }