使用lamda表达式对HashMap进行遍历

Question

问题遇到的现象和发生背景

使用lamda表达式对HashMap进行遍历

用代码块功能插入代码，请勿粘贴截图

package SaveStudentUseHashMap;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class Test01 {
    public static void main(String[] args) {
        Student s1=new Student("张三",20);

        Student s2=new Student("李四",21);
        Student s3=new Student("张三",20);
        Student s4=new Student("王五",33);

        HashMap<Student,String> hashMap=new HashMap<>();
        hashMap.put(s1,"汉族");
        hashMap.put(s2,"回族");
        hashMap.put(s4,"傣族");
       

        Set<Map.Entry<Student, String>> entries = hashMap.entrySet();
//        for (Map.Entry<Student, String> entry : entries) {
//            Student tempStudent=entry.getKey();
//            String  nativePlace=entry.getValue();
//            System.out.println(tempStudent.name+tempStudent.age+nativePlace);
//        }
        
    }
}

Student 类

package SaveStudentUseHashMap;

public class Student {
        String name;
        int age;

    public Student() {
    }

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

    @Override
    public boolean equals(Object obj) {
        Student inputStudent=(Student)obj;
        if(inputStudent.age==this.age&&inputStudent.name.equals(this.name)){
            return true;
        }else{
            return false;
        }

    }
}

Answer 1

如果想使用 lambda 表达式去遍历 HashMap 的话，方法很简单，
HashMap 类自身就有一个 forEach() 方法，直接用这个就行，示例代码如下：

public class Test01 {

    public static void main(String[] args) {
        Student s1=new Student("张三",20);

        Student s2=new Student("李四",21);
        Student s3=new Student("张三",20);
        Student s4=new Student("王五",33);

        HashMap<Student,String> hashMap=new HashMap<>();
        hashMap.put(s1,"汉族");
        hashMap.put(s2,"回族");
        hashMap.put(s4,"傣族");

        // 使用 lamda 表达式遍历 HashMap
        hashMap.forEach((k, v)-> System.out.println(k + ", "+ v));

    }
}

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