Java 面向对象编程示例

Test13 类

package com.oop;

public class Test13 {
    public static void main(String[] args) {
        JavaClass javaClass = new JavaClass(5);
        javaClass.push(new JavaStudent(1, "张三", 18, true));
        javaClass.push(new JavaStudent(2, "李四", 19, false));
        javaClass.push(new JavaStudent(3, "王五", 20, true));
        javaClass.push(new JavaStudent(4, "赵六", 21, false));
        javaClass.push(new JavaStudent(5, "田七", 22, true));

        System.out.println(javaClass.push(new JavaStudent(6, "小明", 22, true)));
        System.out.println(javaClass.push(new JavaStudent(7, "田七", 22, true)));
        System.out.println(javaClass.push(new JavaStudent(8, "田七", 22, true)));
        System.out.println(javaClass.push(new JavaStudent(9, "黑盒", 22, true)));

        System.out.println(javaClass.getJavaClass());
        System.out.println("====================================");
        JavaStudent student = javaClass.find(5)[0];
        System.out.println(student.getStudent());

        System.out.println("====================================");

        javaClass.update(new JavaStudent(5, "牛逼王", 22, true));
        System.out.println(student.getStudent());

        System.out.println("====================================");
        javaClass.delete(3);
        System.out.println(javaClass.getJavaClass());
    }
}

笔者在 Test13 类中创建了一个 JavaClass 对象，并向其中添加了多个 JavaStudent 实例。通过调用 push 方法，学生对象被添加到班级中。当班级容量不足时，push 方法会自动扩展数组的长度。接着，笔者展示了如何查找、更新和删除学生信息，并通过 getJavaClass 方法打印出当前班级的所有学生信息。

JavaClass 类

package com.oop;

import java.util.Arrays;

public class JavaClass {
    private JavaStudent[] students = null;
    private int actualLength = 0;

    public JavaClass() {
        this.students = new JavaStudent[5];
    }

    public JavaClass(int length) {
        this.students = new JavaStudent[length > 0 ? length : 5];
    }

    public int push(JavaStudent student) {
        if (actualLength >= students.length) {
            int newLength = students.length * 2;
            students = Arrays.copyOf(students, newLength);
        }
        students[actualLength++] = student;
        return actualLength;
    }

    public JavaStudent[] find(int sid) {
        for (JavaStudent student : students) {
            if (student != null && student.getSid() == sid) {
                return new JavaStudent[]{student};
            }
        }
        return null;
    }

    public int update(JavaStudent student) {
        JavaStudent existingStudent = find(student.getSid())[0];
        if (existingStudent != null) {
            existingStudent.setName(student.getName());
            existingStudent.setAge(student.getAge());
            existingStudent.setIsEmployed(student.getIsEmployed());
            return existingStudent.getSid();
        }
        return 0;
    }

    public int delete(int sid) {
        for (int i = 0; i < actualLength; i++) {
            if (students[i].getSid() == sid) {
                for (int j = i; j < actualLength - 1; j++) {
                    students[j] = students[j + 1];
                }
                students[actualLength - 1] = null;
                actualLength--;
                return sid;
            }
        }
        return 0;
    }

    public String getJavaClass() {
        StringBuilder stringData = new StringBuilder();
        for (int i = 0; i < actualLength; i++) {
            stringData.append(students[i].getStudent());
        }
        return "[" + stringData.toString() + "]";
    }
}

在 JavaClass 类中，笔者管理了一个 JavaStudent 数组，用于存储学生对象。构造方法允许初始化数组的长度，默认为5。当添加学生时，如果数组已满，push 方法会将数组长度加倍，以容纳更多学生。find 方法通过学生ID查找对应的学生对象，update 方法用于更新学生信息，delete 方法则用于删除指定ID的学生。getJavaClass 方法返回当前班级所有学生的信息。

优化点：

• 将 javaClass 数组重命名为 students，提高变量名的可读性。
• 在 find 方法中增加空值检查，避免潜在的空指针异常。
• 使用 StringBuilder 替代字符串拼接，提高 getJavaClass 方法的性能。

JavaStudent 类

package com.oop;

public class JavaStudent {
    private int sid;
    private String name;
    private int age;
    private boolean isEmployed;

    public JavaStudent() {
    }

    public JavaStudent(int sid, String name, int age, boolean isEmployed) {
        this.sid = sid;
        this.name = name;
        this.age = age;
        this.isEmployed = isEmployed;
    }

    public void setSid(int sid) {
        this.sid = sid;
    }

    public int getSid() {
        return sid;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getAge() {
        return age;
    }

    public void setIsEmployed(boolean isEmployed) {
        this.isEmployed = isEmployed;
    }

    public boolean getIsEmployed() {
        return isEmployed;
    }

    public String getStudent() {
        return "{\n"
                + "\t\"sid\": " + sid + ",\n"
                + "\t\"name\": \"" + name + "\",\n"
                + "\t\"age\": " + age + ",\n"
                + "\t\"isEmployed\": " + isEmployed + "\n"
                + "}\n";
    }
}

JavaStudent 类代表一个学生对象，包含学生ID、姓名、年龄和就业状态等属性。提供了相应的构造方法、getter 和 setter 方法，以及一个 getStudent 方法，用于返回学生信息的字符串表示。

优化点：

• 移除了多余的逗号，确保生成的JSON格式正确。
• 确保 getStudent 方法输出的字符串格式规范，便于阅读和调试。

注意事项

在使用这些类时，确保正确处理可能的 null 值，特别是在调用 find 方法后，返回值可能为 null。在实际应用中，建议增加更多的错误处理和输入验证，以提高程序的健壮性。