studentarraylist.java

ssd3部分quiz、exercise、exam的参考答案

import java.util.*;

/**
 * This class contains methods to process array lists of {@link Student}
 * objects.
 *
 * @author  LiGuoLiang
 * @version  1.0.0
 * @see  Student
 * @see  ArrayList
 */
public class  StudentArrayList  {

	/**
	 * Returns an array list with three elements.
	 *
	 * @param first  a <code>Student</code> object.
	 * @param second  a <code>Student</code> object.
	 * @param third  a <code>Student</code> object.
	 * @return an array list with the objects <code>first</code>,
	 *           <code>second</code>, and <code>third</code>
	 */
	public static ArrayList<Student> makeArrayList(
		Student  first,
		Student  second,
		Student  third)  {

		/* PLACE YOUR CODE HERE */
		ArrayList<Student> array = new ArrayList<Student>();
		array.add(first);
		array.add(second);
		array.add(third);

		return array; // REMOVE; USED SO THIS FILE COMPILES
	}

	/**
	 * Returns an array list with the same elements of the specified array
	 * arranged in the same order.
	 *
	 * @param array  an array with <code>Student</code> objects .
	 * @return an array list with the same elements of the specified array
	 *         arranged in the same order
	 */
	public static ArrayList<Student> makeArrayListFromArray(Student[] array) {

		/* PLACE YOUR CODE HERE */
		ArrayList<Student> anotherArray = new ArrayList<Student>();
		for(Student element : array) {
			anotherArray.add(element);
		}

		return anotherArray; // REMOVE; USED SO THIS FILE COMPILES
	}

	/**
	 * Returns <code>true</code> if the specified array list contains a
	 * student whose id matches the specified ID.
	 *
	 * @param arrayList  an array list of <code>Student</code> objects.
	 * @param id  a student ID.
	 * @return  <code>true</code> if the specified array list contains a
	 *          student whose ID matches the specified ID;
	 *          <code>false</code> otherwise.
	 */
	public static boolean hasStudent(
		ArrayList<Student>  arrayList,
		int  id)  {

		/* PLACE YOUR CODE HERE */
		for(Student element : arrayList) {
			if(element.getId()==id) {
				return true;
			}
		}

		return false; // REMOVE; USED SO THIS FILE COMPILES
	}

	/**
	 * Returns the number of students in the specified array list whose
	 * grade is greater than or equal to the specified grade.
	 *
	 * @param arrayList  an array list of <code>Student</code> objects.
	 * @param grade  a grade.
	 * @return  the number of students in the specified array list whose
	 *          grade is greater than or equal to the specified grade.
	 */
	public static int countGradeGreaterOrEqual(
		ArrayList<Student> arrayList,
		int grade)  {

		/* PLACE YOUR CODE HERE */
		int number = 0;
		for(Student element : arrayList) {
			if(element.getGrade()>=grade) {
				number++;
			}
		}

		return number; // REMOVE; USED SO THIS FILE COMPILES
	}

	/**
	 * Returns the smallest grade of the students in the specified array list.
	 * <p>
	 * This method assumes that the array list is not empty.
	 *
	 * @param arrayList  an array list of <code>Student</code> objects.
	 * @return  the smallest grade of the students in the specified array list.
	 */
	public static int getMinGrade(ArrayList<Student> arrayList)  {

		/* PLACE YOUR CODE HERE */
		int minGrade = 0;
		Iterator<Student> arrayIterator = arrayList.iterator();
		if(arrayIterator.hasNext()) {
			minGrade = arrayIterator.next().getGrade();
		}
		for(;arrayIterator.hasNext();) {
			Student element = arrayIterator.next();
			if(element.getGrade()<minGrade) {
				minGrade = element.getGrade();
			}
		}

		return minGrade; // REMOVE; USED SO THIS FILE COMPILES
	}

	/**
	 * Returns the average grade of the students in the specified array list.
	 *
	 * @param arrayList  an array list of <code>Student</code> objects.
	 * @return  the average grade of the students in the specified array list.
	 */
	public static double getGradeAverage(ArrayList<Student>  arrayList)  {

		/* PLACE YOUR CODE HERE */
		int sum =0;
		double average;
		for(Student element : arrayList) {
			sum += element.getGrade();
		}
		average = ((double)sum)/arrayList.size();

		return average; // REMOVE; USED SO THIS FILE COMPILES
	}

	/**
	 * Removes all students in the specified array list whose grade
	 * is less than the specified grade.
	 *
	 * @param arrayList  an array list of <code>Student</code> objects.
	 * @param grade  a grade.
	 */
	public static void removeGradeLess(
		ArrayList<Student>  arrayList,
		int  grade)  {
			
		/* PLACE YOUR CODE HERE */
		Iterator<Student> arrayIterator = arrayList.iterator();
		ArrayList<Student> temp = new ArrayList<Student>();
		for(;arrayIterator.hasNext();) {
			Student element = arrayIterator.next();
			if(element.getGrade()<grade) {
				temp.add(element);
			}			 
		}
		for(int i=0;i<temp.size();i++) {
			arrayList.removeAll(temp);
		}
		
	}

	/**
	 * Returns the string representation of the objects in the specified
	 * array list.
	 * <p>
	 * A new line character ( \n ) should separate the string
	 * representations of the objects. For example:
	 * </p>
	 * <pre>
	 * Student[328,Galileo Galilei,80]\nStudent[123,Albert Einstein,100]
	 * </pre>
	 * <p>
	 * Note that the string does <i>not</i> end with a new line character ( \n )
	 * </p>
	 *
	 * @param arrayList  an array list of <code>Student</code> objects.
	 * @return  the string representation of the objects in the specified
	 *          array list.
	 */
	public static String displayAll(ArrayList<Student>  arrayList)  {

		/* PLACE YOUR CODE HERE */
		String result = "";
		for(int i=0;i<arrayList.size()-1;i++) {
			result += arrayList.get(i).toString()+"\n";
		}
		result += arrayList.get(arrayList.size()-1).toString();
		
		return result; // REMOVE; USED SO THIS FILE COMPILES
	}
}