使用工具

IDEA2018.2

使用說(shuō)明

使用迭代器，即創(chuàng)建Iterator對(duì)象，Iterator是一個(gè)接口，也有泛型

hasNext方法判斷是否已經(jīng)遍歷完，

next方法取當(dāng)前遍歷的對(duì)象

HashMap用keySet()方法獲得鍵的Set集合

values()方法獲得值的Set集合

entrySet()方法獲得鍵值對(duì)的Set集合

代碼示例

Student.java

package com.vvcat;/*** @Author ??VVcat??* @Date 2019/10/13 19:37* @Version 1.0**/ public class Student {private Integer id;private String name;private String sex;private Integer age;public Student() {}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Student(Integer id, String name) {this.id = id;this.name = name;}public Student(Integer id, String name, String sex, Integer age) {this.id = id;this.name = name;this.sex = sex;this.age = age;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Overridepublic String toString() {return "Student{" +"id=" + id +", name='" + name + '\'' +", sex='" + sex + '\'' +", age=" + age +'}';} }

HashMap .java

package com.vvcat;import java.util.*;/*** @Author ??VVcat??* @Date 2019/10/13 19:39* @Version 1.0**/public class HashMap {public static void main(String[] args) {//實(shí)例化3個(gè)學(xué)生Student stu1 = new Student(1, "張三","男",20);Student stu2 = new Student(2, "李四","男",21);Student stu3 = new Student(3, "趙五","男",22);// 實(shí)例化HashMap用于保存學(xué)生java.util.HashMap<Integer, Student> map = new java.util.HashMap<Integer, Student>();//建立學(xué)號(hào)與學(xué)生的映射關(guān)系map.put(stu1.getId(),stu1);map.put(stu2.getId(),stu2);map.put(stu3.getId(),stu3);// 遍歷方法1.通過Map.keySet遍歷key和value(經(jīng)常使用，二次取值)Set<Integer> keys = map.keySet();Iterator<Integer> it1 = keys.iterator();System.out.println("遍歷方法1，通過keySet遍歷key和value獲得鍵集合 ");for (Integer key : map.keySet()) {System.out.println("key = "+ key + " and value= " + map.get(key));}while (it1.hasNext()){Student st = map.get(it1.next());System.out.println("學(xué)號(hào)：" + st.getId() + "\t" + "姓名：" + st.getName() + "\t" + "性別：" + st.getSex() + "\t" + "年齡：" + st.getAge());}System.out.println("---------------------------");// 遍歷方法2.通過Map.values()遍歷所有的value，但不能遍歷keyCollection<Student> values = map.values();Iterator<Student> it2 = values.iterator();System.out.println("遍歷方法2,通過values獲得值集合");for (Student stu : map.values()) {System.out.println("value= " + stu);}while(it2.hasNext()){Student next = it2.next();System.out.println("學(xué)號(hào)：" + next.getId() + "\t"+ "姓名：" + next.getName()+ "\t" + "性別：" + next.getSex() + "\t"+ "年齡：" + next.getAge());}System.out.println("---------------------------");// 遍歷方法3.通過Map.entrySet使用iterator遍歷key和value：Set<Map.Entry<Integer, Student>> kys = map.entrySet();Iterator<Map.Entry<Integer, Student>> it3 = kys.iterator();System.out.println("遍歷方法3，通過entrySet使用iterator遍歷key和value獲得鍵值對(duì)");while(it3.hasNext()){Student st = it3.next().getValue();System.out.println("學(xué)號(hào)：" + st.getId() + "\t" + "姓名：" + st.getName()+ "\t" + "性別：" + st.getSex()+ "\t" + "年齡：" + st.getAge());}System.out.println("---------------------------");//遍歷方法4：通過Map.entrySet遍歷key和value(推薦容量大時(shí)使用)System.out.println("通過Map.entrySet遍歷key和value");for (Map.Entry<Integer, Student> entry : map.entrySet()) {Student st = entry.getValue();System.out.println("學(xué)號(hào)：" + entry.getKey()+ "\t" + "姓名：" + st.getName()+ "\t" + "性別：" + st.getSex()+ "\t" + "年齡：" + st.getAge());}} } 《新程序員》：云原生和全面數(shù)字化實(shí)踐50位技術(shù)專家共同創(chuàng)作，文字、視頻、音頻交互閱讀

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