Question

我正在努力找到相关的答案来解决我的问题。我有一个数组列表：

List<Teacher> teacherList = new ArrayList<Teacher>(11);

教师班级具有名称属性。我想浏览教师列表，找出是否有与用户输入名称匹配的名称。

例如，

Scanner teacherNameScanner = new Scanner (System.in);
System.out.println("What is the teachers name");
teacherName = teacherNameScanner.nextLine();

/* Here I want to scan through the teacherList and see whether the name entered
matches the name of any of the teachers. If it does not match I want to tell the
user to enter a correct name */

Answer 1

这实际上取决于您的用例，名称是否区分大小写？另外，您可能需要考虑修剪空间。然后创建一个Set nameSet，您可以在其中获取O（1）操作的现有名称。同样，对此有很多解决方案，除非您描述确切的用例，例如您是否想用姓名或ID（通常是ID）来确定教师，否则很难找到正确的解决方案。但是使用您描述的HashSet应该做的事情。

Set<String> nameSet = new HashSet<String>();

if (nameSet.contains(teacherName))
   do what you want
else
   other case

Answer 2

for each正是医生所订购的（除非您有一些特别的命令，您可以使用它进行更有效的搜索）。

private Teacher findTheTeacher(ArrayList<Teacher> teacherList, String teacherName) {

    for (Teacher teacher : teacherList) {
        if (teacher.name.equals(teacherName)) {
            return teacher;
        }
    }
    return null; // or something like this
}

Answer 3

要扫描teacherList并查找是否与输入的老师姓名（teacherName）相匹配，可以使用以下方法之一。请注意，每种方法都将teacherList和enteredName作为参数，并返回boolean是或否-取决于是否找到匹配项。

共有三种方法，每种方法的执行方式都不相同。请注意，第三个结构C-使用与前两个结构A和B不同的方法。

方法A：

使用for循环迭代teacherList并查找是否有名称匹配的教师：

for (Teacher teacher : teacherList) {
    if (teacher.getName().equals(enteredName)) {
        // a match is found
        return true;
    }
}

return false;

方法B：

它具有与方法A相同的功能，但使用不同的代码构造-流和lambda：

boolean enteredTeacherExists =  teacherList.stream()
                                           .anyMatch(teacher -> teacher.getName().equals(enteredName));

语法teacher -> teacher.getName().equals(enteredName)是Predicate<Teacher>类型的lambda表达式。

方法C：

此方法使用另一种方法。无需测试老师的姓名，而是使用输入的姓名构造老师对象，然后使用该对象查找匹配项。

使用输入的名称创建一名教师，并测试列表中是否存在该教师。

Teacher enteredTeacher = new Teacher(enteredName);
boolean enteredTeacherExists = teacherList.contains(enteredTeacher);

如果列表中存在同名老师，则返回的值为true，否则为false。

请注意，Teacher类（请参见下面的定义）具有java.lang.Object类的重写equals()方法。此方法指定两个教师对象相等的条件-如果它们的名称相等，则认为教师对象相等。这允许使用等于List的{{1}}方法。

代码：

Teacher.java：

contains

TeacherTester.java

public class Teacher {

    private String name;

    public Teacher(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    @Override
    /* This returns a string representation of the teacher - the name. */
    public String toString() {
        return name;
    }

    @Override
    public boolean equals(Object other) {
        if ((other != null) && (other instanceof Teacher)) {
            Teacher otherTeacher = (Teacher) other;
            if (otherTeacher.getName().equals(this.name)) {
                return true;
            }
        }
        return false;
    }
}

输出：

public class TeacherTester {

    public static void main(String [] args) {

        // Create some teachers
        Teacher teacher1 = new Teacher("first");
        Teacher teacher2 = new Teacher("second");
        Teacher teacher3 = new Teacher("third");
        List<Teacher> teacherList = Arrays.asList(teacher1, teacher2, teacher3);

        System.out.println("Teachers: " + teacherList);

        // Look for teacher - using method A
        String enteredName = "ninth";
        System.out.println("A. Found " + enteredName + " : " + findTeacherA(teacherList, enteredName));
        enteredName = "first";
        System.out.println("A. Found " + enteredName + " : " + findTeacherA(teacherList, enteredName));

        // Look for teacher - using method B
        enteredName = "ninth";
        System.out.println("B. Found " + enteredName + " : " + findTeacherB(teacherList, enteredName));
        enteredName = "second";
        System.out.println("B. Found " + enteredName + " : " + findTeacherB(teacherList, enteredName));

        // Look for teacher - using method C
        enteredName = "third";
        System.out.println("C. Found " + enteredName + " : " + findTeacherC(teacherList, enteredName));
        enteredName = "ninth";
        System.out.println("C. Found " + enteredName + " : " + findTeacherC(teacherList, enteredName));     

    }

    private static boolean findTeacherA(List<Teacher> teacherList, String enteredName) {

        for (Teacher teacher : teacherList) {

            if (teacher.getName().equals(enteredName)) {
                // a match is found
                return true;
            }
        }

        return false;
    }

    private static boolean findTeacherB(List<Teacher> teacherList, String enteredName) {

        return teacherList.stream()
                            .anyMatch(teacher -> teacher.getName().equals(enteredName));
    }

    private static boolean findTeacherC(List<Teacher> teacherList, String enteredName) {

        Teacher enteredTeacher = new Teacher(enteredName);
        return teacherList.contains(enteredTeacher);
    }
}

Answer 4

在 Java8 中，您可以使用流：

public static Teacher findByName(Collection<Teacher> teachers, String name) {
    return teachers.stream().filter(teacher -> teacher.getName().equals(name)).findFirst().orElse(null);
}

此外，如果您有许多不同的对象（不仅是Teacher），或者想通过不同的属性（不仅是name查找它，还可以构建一个实用程序类来封装其中的逻辑：

public final class FindUtils {
    public static <T> T findByProperty(Collection<T> col, Predicate<T> filter) {
        return col.stream().filter(filter).findFirst().orElse(null);
    }
}

public final class TeacherUtils {
    public static Teacher findByName(Collection<Teacher> teachers, String name) {
        return FindUtils.findByProperty(teachers, teacher -> teacher.getName().equals(name));
    }

    public static Teacher findByAge(Collection<Teacher> teachers, int age) {
        return FindUtils.findByProperty(teachers, teacher -> teacher.getAge() == age);
    }

}

Answer 5

如果您使用的是Java 8或更高版本，则可以使用：

teacherList.stream().anyMatch(teacher -> teacher.getName().equals(name));

其中name是您要搜索的名称。

Java-在遍历对象列表的同时搜索特定属性

5 个答案: