HashMap使用范例

HashMapDemo.java

package corejava8.structure;

import java.util.HashMap;
import java.util.Map;

public class HashMapDemo {
  public static void main(String[] argv) {
    // Construct and load the hash. This simulates loading a
    // database or reading from a file, or wherever the data is.

    Map<String,String> map = new HashMap<String,String>();

    // The hash maps from company name to address.
    // In real life this might map to an Address object...
    map.put("Adobe", "Mountain View, CA");
    map.put("IBM", "White Plains, NY");
    map.put("Learning Tree", "Los Angeles, CA");
    map.put("Microsoft", "Redmond, WA");
    map.put("Netscape", "Mountain View, CA");
    map.put("O'Reilly", "Sebastopol, CA");
    map.put("Sun", "Mountain View, CA");

    // Two versions of the "retrieval" phase.
    // Version 1: get one pair's value given its key
    // (presumably the key would really come from user input):
    String queryString = "O'Reilly";
    System.out.println("You asked about " + queryString + ".");
    String resultString = map.get(queryString);
    System.out.println("They are located in: " + resultString);
    System.out.println();

    // Version 2: get ALL the keys and values 
    // (maybe to print a report, or to save to disk)
    for( String key : map.keySet()) {
    	System.out.println("Key " + key + "; Value " + map.get(key));
    }
    
    // Version 3: Same but using a Map.Entry lambda
    map.entrySet().forEach(mE -> 
        System.out.println("Key + " + mE.getKey() + "; Value " +mE.getValue()));
  }
}

运行结果:
You asked about O'Reilly.
They are located in: Sebastopol, CA

Key IBM; Value White Plains, NY
Key Learning Tree; Value Los Angeles, CA
Key O'Reilly; Value Sebastopol, CA
Key Microsoft; Value Redmond, WA
Key Adobe; Value Mountain View, CA
Key Sun; Value Mountain View, CA
Key Netscape; Value Mountain View, CA
Key + IBM; Value White Plains, NY
Key + Learning Tree; Value Los Angeles, CA
Key + O'Reilly; Value Sebastopol, CA
Key + Microsoft; Value Redmond, WA
Key + Adobe; Value Mountain View, CA
Key + Sun; Value Mountain View, CA
Key + Netscape; Value Mountain View, CA