LinkedList遍历输出重复最后元素：如何获取节点多字段值？

问题描述 #

我实现的LinkedList中每个节点包含StudentID、Group、Priority三个字段，重写toString()方法遍历链表时，始终输出最后一个学生的信息，而非对应节点的内容，求修改方案。

原代码 #

public String toString() {
    System.out.println("--------------------------------------");
    String str = " ";

    ListNode current = head;
    while (current != null) {
        str += "StudentID: " + StudentAdd.getStudentID() + " is in Group " +
            StudentAdd.getGroup().toUpperCase() + " with priority " + 
            StudentAdd.getPriority();
            str += "]\n";
            current = current.getNext();

        }
        
        return str;
    }

期望输出 #

[StudentID:0001 is in Group A with Priority 1]
[StudentID:0005 is in Group C with Priority 1]
[StudentID:0220 is in Group B with Priority 2]
[StudentID:0200 is in Group B with Priority 2]
[StudentID:0215 is in Group B with Priority 2]
[StudentID:0315 is in Group B with Priority 3]
[StudentID:0301 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]

实际输出 #

[StudentID:0350 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]
[StudentID:0350 is in Group B with Priority 3]

问题原因及修复方案 #

问题核心：你当前代码调用的StudentAdd.getStudentID()这类方法，是获取全局/静态的最后一次添加的学生数据，而非当前遍历节点的学生信息。必须从当前遍历的current节点中取出对应Student实例，再调用其get方法。

另外补充两个优化点：

• 字符串拼接用StringBuilder替代直接+=，避免频繁创建字符串对象，提升效率
• 修复输出格式，补上缺失的[符号，和期望输出对齐

修改后的代码 #

public String toString() {
    System.out.println("--------------------------------------");
    StringBuilder str = new StringBuilder();

    ListNode current = head;
    while (current != null) {
        // 从当前节点获取对应的Student对象
        Student student = current.getStudent();
        str.append("[StudentID: ")
           .append(student.getStudentID())
           .append(" is in Group ")
           .append(student.getGroup().toUpperCase())
           .append(" with priority ")
           .append(student.getPriority())
           .append("]\n");
        current = current.getNext();
    }
    
    return str.toString();
}

注：假设你的ListNode类中存在getStudent()方法，用于返回该节点存储的Student实例；如果节点直接存储三个字段（而非Student对象），则直接调用current.getStudentID()、current.getGroup()、current.getPriority()即可。

内容的提问来源于stack exchange，提问作者Alex