两个小例子

1、输入某年某月某日，判断这一天是这一年的第几天

Scanner scanner = new Scanner(System.in);
System.out.println("请输入日期，格式是yyyy-MM-dd");
String data = scanner.next();
String[] datas = data.split("-");
int year = Integer.valueOf(datas[0]);
int month = Integer.valueOf(datas[1]);
int day = Integer.valueOf(datas[2]);
int sum = 0;
for (int i = 1;i<month;i++){
    if(i==1||i==3||i==5||i==7||i==8||i==10||i==12){
        sum+=31;
    }else if(i==4||i==6||i==9||i==11){
        sum+=30;
    }else if(i==2){
        //判断是否为闰年
        if(year%4==0&&year%100!=0||year%400==0){
            sum+=29;
        }else {
            sum+=28;
        }
    }

}
sum=sum+day;
System.out.println(data+"是"+year+"的第"+sum+"天");

2.录入本班学生姓名，成绩，自动计算出平均分，并且得出第一名。

Scanner scanner = new Scanner(System.in);
Map<String, String> str = null;
List<Map<String, String>> stuliList = new ArrayList<Map<String, String>>();
//输入多个数字，求其总和
for(int i = 1;i<5;i++){
    System.out.println("请输入第"+i+"个姓名：");
    String name = scanner.next();
    System.out.println("请输入第"+i+"个成绩：");
    String score = scanner.next();
    str = new HashMap<String, String>();
    //HashMap键值对的方式使用put添加元素
    str.put("name", name);
    str.put("score", score);
    stuliList.add(str);
}
System.out.println(stuliList.size());

Double sum = 0D;
Double avg = 0D;
Double max = 0D;

for (Map<String, String> salmap : stuliList) {

    //获取集合中的薪资
    String score = salmap.get("score");
    Double sumscore = Double.parseDouble(score);
    System.out.println("成绩：" + score);
    //计算和
    sum += sumscore;
    System.out.println("SUM：" + sum);
    //计算平均值
    avg=sum/stuliList.size();
    System.out.println("avg：" + avg);

    for(int i = 0;i<salmap.size();i++){
    /*   if(sumscore>max){
            max=sumscore;
        }*/
        max = Math.max(max,sumscore);
    }

    System.out.println("最大值：" + max);

}