Java:统计一个值被输入的次数

Question

我正在寻找一种方法来计算 Java 中输入值的次数。更具体地说，我必须管理一个 Module 类，它具有以下属性:semester 和 code。如果它是第 1 学期添加的第一个模块，则其代码应为 101。该学期的第二个模块的代码将为 102，同样，第 2 学期输入的第一个模块的代码将为 201，依此类推。

我尝试使用静态实例变量count，但我无法以某种方式设法使其根据输入的学期值进行更改。

如有任何建议，我们将不胜感激。提前致谢!

--编辑--

下面是我的类(class)的完整代码。如果太长，我很抱歉。

    package courseman;

/**
 * @overview   <code>Module</code> represents the module object of a CourseMan program
 * @author
 *
 */
public class Module {
    private static int count = 1;
    private String name;
    private int semester;
    private int credits;
    private String code;

/**
 * @effects   Initializes a <code>Module</code> object
 * 
 */
public Module(){
    name = "No name";
    semester = 1;
    credits = 0;
    code = "M000";
}

/**
 * @param newModule   a <code>Module</code> object
 * @effects           Creates a <code>Module</code> object with <code>newModule</code>
 * 
 */
public Module (Module newModule){
    if (newModule == null){
        System.out.println("Fatal error creating module.");
        System.exit(0);
    }
    name = newModule.name;
    semester = newModule.semester;
    credits = newModule.credits;
    code = newModule.code;
}

/**
 * 
 * @param newName       a <code>String</code> to be set as a module's name
 * @param newSemester   an <code>integer</code> to be set as a module's semester
 * @param newCredits    an <code>integer</code> to be set as a module's credits
 * @effects             Creates a new <code>Module</code> object with predefined name, semester and credits 
 */
public Module(String newName, int newSemester, int newCredits){
    if(newName == null || newSemester <= 0 || newCredits <= 0){
        System.out.println("Fatal error creating module.");
        System.exit(0);
    }
    name = newName;
    semester = newSemester;
    credits = newCredits;

    int no = semester*100 + count;
    code = "M" + no;
    count++;
}

/**
 * 
 * @param newName   a <code>String</code> to be set as a module's name
 * @modifies        <code>this.name</code>
 * @effects         Takes <code>newName</code> to update a module's name
 * 
 */
public void setName(String newName){
    if(newName == null){
        System.out.println("Fatal error setting module's name.");
        System.exit(0);
    }
    name = newName;
}

/**
 * 
 * @param newSemester   an <code>int</code> to be set as a module's semester
 * @modifies            <code>this.semester</code>
 * @effects             Takes <code>newSemester</code> to update a module's semester
 * 
 */
public void setSemester(int newSemester){
    if (newSemester <= 0){
        System.out.println("Fatal error setting module's semester.");
        System.exit(0);
    }
    semester = newSemester;
    int no = (int) Integer.parseInt(code.substring(1));
    if (((no - count - 1)/100) < semester){
        no = semester*100 + (count - 1);
        code = "M" + no;
    }
}

/**
 * 
 * @param newCredits    an <code>integer</code> to be set as a module's number of credits
 * @modifies            <code>this.credits</code>
 * @effects             Takes <code>newCredits</code> to update a module's number of credits
 * 
 */
public void setCredits (int newCredits){
    if (newCredits <= 0){
        System.out.println("Fatal error setting module's credits.");
        System.exit(0);
    }
    credits = newCredits;
}

/**
 * 
 * @effects   Returns a module's code
 */
public String getCode(){
    return code;
}

/**
 * @effects   Returns a module's name
 * 
 */
public String getName(){
    return name;
}

/**
 * @effects   Returns a module's semester
 * 
 */
public int getSemester(){
    return semester;
}

/**
 * @effects   Returns a module's number of credits
 * 
 */
public int getCredits(){
    return credits;
}

/**
 * @effects   Returns <code>String</code> representation of a <code>Module</code> object
 */
public String toString(){
    return "Module: " + code + " - " + name + " - semester " + semester + " - " + credits + " credits";
}

/**
 * 
 * @param otherModule   a <code>Module</code> object to compare
 * @effects             Returns <code>true</code> if <code>this</code> points to the same
 *                      object as <code>otherModule</code>, otherwise returns <code>false</code>
 */
public boolean equals(Module otherModule){
    return (code.equals(otherModule.code));
}

}

Answer 1

您应该为学期管理一个单独的柜台!尝试使用静态 HashMap 将学期映射到该学期的类(class)数量。添加新的模块时，您需要增加适当的计数(如果不存在，则将其初始化为1)。

这是一个骨架:

class Module {
    private static HashMap<Integer, Integer> courseCounts = new HashMap<Integer, Integer>();

    public Module(int semester, String name) {
        this.semester = semester;
        this.name = name;
        Integer count = courseCounts.get(semester);
        if (count == null)
            count = 0;
        ++count;
        this.code = "M" + (semester * 100 + count);
        courseCounts.put(semester, count);
    }
}