弹吉他的兔子
在本文中，我们将通过示例讨论在 Java 上遍历 HashMap 的五种最佳方法。
- 使用 Iterator 遍历 HashMap EntrySet
- 使用 Iterator 遍历 HashMap KeySet
- 使用 For-each 循环迭代 HashMap
- 使用 Lambda 表达式遍历 HashMap
- 使用 Stream API 遍历 HashMap
1、使用Iterator 遍历HashMap EntrySet
package com.jude.iterations;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
/**
* 在Java中遍历HashMap的5种最佳方法
* @Author jude
* @Date 2020/7/5 12:41 PM
* @Version 1.0
*/
public class IterateHashMapExample {
public static void main(String[] args) {
Map<Integer,String> courseMap = new HashMap<Integer, String>();
courseMap.put(1,"C");
courseMap.put(2,"C++");
courseMap.put(3,"Java");
courseMap.put(4,"Spring MVC");
courseMap.put(5,"Hibernate ORM framework");
// 1. 使用 Iterator 遍历 HashMap EntrySet
Iterator<Map.Entry<Integer, String>> iterator = courseMap.entrySet().iterator();
while (iterator.hasNext()){
Map.Entry<Integer, String> entry = iterator.next();
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
}
}
Output:
2. 使用 Iterator 遍历 HashMap KeySet
public class IterateHashMapExample {
public static void main(String[] args) {
Map<Integer,String> courseMap = new HashMap<Integer, String>();
courseMap.put(1,"C");
courseMap.put(2,"C++");
courseMap.put(3,"Java");
courseMap.put(4,"Spring MVC");
courseMap.put(5,"Hibernate ORM framework");
// 2. 使用 Iterator 遍历 HashMap KeySet
Iterator<Integer> iterator2= courseMap.keySet().iterator();
while (iterator2.hasNext()){
Integer key = iterator2.next();
System.out.println(key);
System.out.println(courseMap.get(key));
}
}
}
Output:
3、使用 For-each 循环遍历 HashMap
public class IterateHashMapExample {
public static void main(String[] args) {
Map<Integer,String> courseMap = new HashMap<Integer, String>();
courseMap.put(1,"C");
courseMap.put(2,"C++");
courseMap.put(3,"Java");
courseMap.put(4,"Spring MVC");
courseMap.put(5,"Hibernate ORM framework");
// 3、使用 For-each 循环遍历 HashMap
for (Map.Entry<Integer,String> entry : courseMap.entrySet()) {
System.out.println(entry.getKey());
System.out.println(entry.getValue());
}
}
}
Output:
4、使用Lambda表达式遍历HashMap
public class IterateHashMapExample {
public static void main(String[] args) {
Map<Integer,String> courseMap = new HashMap<Integer, String>();
courseMap.put(1,"C");
courseMap.put(2,"C++");
courseMap.put(3,"Java");
courseMap.put(4,"Spring MVC");
courseMap.put(5,"Hibernate ORM framework");
// 4、使用Lambda表达式遍历 HashMap
courseMap.forEach((key,value) -> {
System.out.println(key);
System.out.println(value);
});
}
}
Output:
5、使用Stream API 遍历HashMap
public class IterateHashMapExample {
public static void main(String[] args) {
Map<Integer,String> courseMap = new HashMap<Integer, String>();
courseMap.put(1,"C");
courseMap.put(2,"C++");
courseMap.put(3,"Java");
courseMap.put(4,"Spring MVC");
courseMap.put(5,"Hibernate ORM framework");
// 5、使用Stream API 遍历HashMap
courseMap.entrySet().stream().forEach(entry -> {
System.out.println(entry.getKey());
System.out.println(entry.getValue());
});
}
}
Output: