用Java初始化HashMap
HashMap类使用哈希表实现Map接口。这使得基本操作（例如get()和put()）的执行时间即使对于大型集合也保持恒定。
以下是HashMap类支持的构造函数的列表。
该构造函数构造一个默认的HashMap。
此构造函数通过使用给定Map对象m的元素来初始化哈希映射。
此构造函数将哈希映射的容量初始化为给定的整数值，容量。
此构造函数使用其参数初始化哈希映射的容量和填充率。
以下是显示如何在Java中初始化和使用HashMap的示例-
示例
import java.util.*;
public class Demo {
public static void main(String args[]) {
HashMap<Integer, String> hashMap = new HashMap<Integer, String>(7);
hashMap.put(1, "Laptop");
hashMap.put(2, "LCD");
hashMap.put(3, "LED");
hashMap.put(4, "Desktop");
hashMap.put(5, "Laptop");
hashMap.put(6, "Notebook");
hashMap.put(7, "Mobile");
System.out.println("HashMap = " + hashMap);
}
}输出结果
HashMap = {1=Laptop, 2=LCD, 3=LED, 4=Desktop, 5=Laptop, 6=Notebook, 7=Mobile}让我们看另一个例子-
示例
import java.util.*;
public class Main {
public static void main(String args[]) {
HashMap hashMap = new HashMap();
hashMap.put("John", new Integer(10000));
hashMap.put("Tim", new Integer(25000));
hashMap.put("Adam", new Integer(15000));
hashMap.put("Katie", new Integer(30000));
hashMap.put("Jacob", new Integer(45000));
hashMap.put("Steve", new Integer(23000));
hashMap.put("Nathan", new Integer(25000));
hashMap.put("Amy", new Integer(27000));
Set set = hashMap.entrySet();
Iterator iterator = set.iterator();
while(iterator.hasNext()) {
Map.Entry map = (Map.Entry)iterator.next();
System.out.print(map.getKey() + ": ");
System.out.println(map.getValue());
}
System.out.println();
System.out.println("Size of IdentintyHashMap: "+hashMap.size());
int bonus = ((Integer)hashMap.get("Amy")).intValue();
hashMap.put("Amy", new Integer(bonus + 5000));
System.out.println("Amy's salary after bonus = " + hashMap.get("Amy"));
int deductions = ((Integer)hashMap.get("Steve")).intValue();
hashMap.put("Steve", new Integer(deductions - 3000));
System.out.println("Steve's salary after deductions = " + hashMap.get("Steve"));
}
}输出结果
Adam: 15000 Nathan: 25000 Katie: 30000 Steve: 23000 John: 10000 Tim: 25000 Amy: 27000 Jacob: 45000 Size of IdentintyHashMap: 8 Amy's salary after bonus = 32000 Steve's salary after deductions = 20000