Java-在迭代对象列表时搜索特定属性[重复]

Question

我正在努力寻找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);

教师类具有名称属性。我想浏览一下教师列表，看看是否有一个名称与用户输入的名称匹配。

那么比如说,，

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

要扫描教师列表并查找输入的教师名称（教师名称）是否匹配，可以使用以下方法之一。请注意，每个方法都将TalerList和enteredName作为参数，并返回一个布尔值true或false--取决于是否找到匹配项。

有三种方法，每种方法的性能都不同。注意第三个构造C——它使用的方法与前两个不同——A和B。

方法A：

使用for循环迭代teacherList，查找是否有姓名匹配的教师：

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

return false;

方法B：

这与方法A具有相同的功能，但使用不同的代码构造流和lambdas：

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

语法老师-


方法C：

此方法使用不同的方法。与测试教师姓名不同，教师对象使用输入的名称构造，对象用于查找匹配项。

从输入的名称创建一个教师，并测试它是否存在于列表中。

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

如果列表中存在同名教师，则返回的值为true，否则为false。

请注意，Teacher类（见下面的定义）有一个java。lang.Object类的重写equals（）方法。此方法指定两个教师对象相等的标准-如果它们的名称相等，则认为教师对象相等。这允许使用equalsList的contains方法。


代码：

教师爪哇：

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;
    }
}


教师测试员。JAVA

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);
    }
}


输出：

Teachers: [first, second, third]
A. Found ninth : false
A. Found first : true
B. Found ninth : false
B. Found second : true
C. Found third : true
C. Found ninth : false

Answer 2

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（不仅仅是Teacher），或者您希望通过不同的属性（不仅仅是name）找到它，您可以构建一个实用程序类，在其中封装此逻辑：

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 3

这取决于您的用例，名称是否区分大小写？此外，您可能需要考虑修剪空间。然后创建一个集合名称集，在其中可以对现有名称执行get操作，这是一个O（1）操作。同样，有很多解决方案，除非你描述了确切的用例，比如你是否想用名字或id（通常是id）来识别一个老师——很难找到正确的解决方案。但是使用您描述的HashSet应该做什么。

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

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