طلب مساعدة في الجافا.........

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السلام عليكم
ممكن أحد يشرح لي فكرة هذي البرامج..
وجزاكم الله ألف خير.

1-Leap Year
Design and implement an application that reads an integer value representing a year from the user. The purpose of the program is to determine if the year is a leap year(and therefore has 29 days in February) in the Gregorian calendar. A year will be a leap year if it is divisible by 4 but not by 100. If a year is divisible by 4 and by 100, it is not a leap year unless it is also divisible by 400. For example, the year 2003 is not a leap year, but 2004 is. The year 1900 is not a leap year because it is divisible by 100, but the year 2000 is a leap year because even though it is divisible by 100, it is also divisible by 400. Produce and error message for any input value less than 1582 (the year the Gregorian calendar was adopted).
2-Flights
Design and implement a class called Flight that represents an airline flight. It should contain instance data that represents the airline name, flight number, and the flight's origin and destination cities. Define the Flight constructor to accept and initialize all instance data. Include getter and setter methods for all instance data. Include a toString method that returns a one-line deion of the flight. Create a driver class called FlightTest, whose main method instantiates and updates several (at least 5) Flight objects.
3-Simple Calculator
Write a program that will evaluate simple expressions such as 17 + 3 and 3.14159 * 4.7. The expressions are to be typed in by the user. The input always consist of a number, followed by an operator, followed by another number. The operators that are allowed are +, -, *, and /. Your program should read an expression, print its value, read another expression, print its value, and so on. The program should end when the user enters 0 as the first number on the line.
4- Team Roster
Create a program called TeamRoster that uses a class called Roster. Roster should contain a team name and the names of all the players on the team written into one string. Use a method called addTeamMember() to append a new member to your roster string. After creating two rosters with more than 5 members.You should indicate the total number of members in each group near the bottom and label each person with an index (e.g. 1,2,3...), print out the team names and their rosters as show below:

Instructors
1. Aalaa
2. Maha
3. Lamar
4. Sahar
5. Nouf
6. Basma
7. Al-anood
Total Members: 7

Students
1. Student 1
2. Student 2
3. Student 3
4. Student 4
5. Student 5
Total Members: 5