标签：nta == put map entry hash java key item
摘要：作为HashMap系列学习笔记的开篇，我认为要先熟悉HashMap的使用场景。
==========================================================================================
Map本质上还是属于集合类型的数据结构。
下面的代码段演示了Map的常用操作（CURD），注意遍历Map尽量使用Entry方式。
1 HashMap<String, Double> scores = new HashMap<>(); 2 3 scores.put("Sam", 100.0); 4 scores.put("Jacky", 50.0); 5 scores.put("Tim", 80.0); 6 7 System.out.print(scores); 8 9 scores.put("Tim", 100.0); 10 System.out.print(scores); 11 System.out.print(scores.toString()); 12 13 System.out.print(scores.get("Sam")); 14 15 System.out.println(scores.containsKey("Sam")); 16 System.out.println(scores.containsValue(100.0)); 17 18 //traverse, cost more time 19 Iterator<String> it = scores.keySet().iterator(); 20 while(it.hasNext()) { 21 String tmp = it.next(); 22 System.out.println(tmp); 23 System.out.println(scores.get(tmp)); 24 } 25 26 System.out.println("count of student:" + scores.size()); 27 System.out.println("scores is " + (scores.isEmpty() ? "empty" : "not empty")); 28 29 //traverse and delete target, cost less 30 Iterator<Map.Entry<String, Double>> begIt = scores.entrySet().iterator(); 31 for(; begIt.hasNext(); ) { 32 Map.Entry<String, Double> item = begIt.next(); 33 34 if(item.getValue() == 100.0) { 35 begIt.remove(); 36 } 37 } 38 39 System.out.println(scores); 40 41 scores.clear(); 42 System.out.println(scores);
输出如下：
{Tim=80.0, Jacky=50.0, Sam=100.0}{Tim=100.0, Jacky=50.0, Sam=100.0}{Tim=100.0, Jacky=50.0, Sam=100.0}100.0true
true
Tim
100.0
Jacky
50.0
Sam
100.0
count of student:3
scores is not empty
{Jacky=50.0}
{}
PS:实际项目中HashMap用的不多，复杂的操作（如key为HashMap）就不做演示了。
标签：nta == put map entry hash java key item
原文地址：http://www.cnblogs.com/buffalo/p/7892807.html
