Java Collection Framework 中List 和 Map遍历总结

Java中在编写代码时一定会涉及到相应数据结构的遍历问题，本文着重Collection框架中的Map和List的遍历

List

• 采用三种方法，根据需求采用即可

        // create list
        List<String> list = new ArrayList<String>();
        // add elements
        list.add("First Day");
        list.add("Second Day");
        list.add("Third Day");

        /**
         *  traversal
         */
        /** 1 */
        for (String str : list) {
            System.out.println(str);
        }

        /** 2  To Array*/
        String [] strArray = new String[list.size()];
        list.toArray(strArray); // create array

        for (int i = 0; i < strArray.length; i++) {
            System.out.println(i + " | "+strArray[i]);
        }

        /** 3 iterator */
        Iterator<String> it = list.iterator(); // iterator
        while (it.hasNext()) {
            System.out.println(it.next());
        }

---

Map

• 采用四种方法

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

        // add elements
        map.put("<1>", "First Day");
        map.put("<2>", "Second Day");
        map.put("<3>", "Third Day");

        /**
         * Traversal
         */
        /** 1   keyset */
        for (String  key : map.keySet()) {
            System.out.println(key+" | "+map.get(key));
        }

        /** 2  通过Map.entrySet使用iterator遍历key和value： */
        Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<String,String> entry = it.next();
            System.out.println("Key: "+entry.getKey()+" | Value: "+entry.getValue());
        }

        /** 3 通过Map.entrySet遍历key和value    ...推荐，尤其是容量大时 */
        for (Map.Entry<String, String> entry : map.entrySet()) {
            System.out.println("Key: "+entry.getKey()+" | Value: "+entry.getValue());
        }

        /** 4 通过Map.values()遍历所有的value，但不能遍历key */
        for (String str : map.values()) {
            System.out.println(str);
        }

---

完整测试代码：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;



/**
 * 
 * @author Henry
 *
 * Desc: List Test
 */
class MyList {
    public void MyListShow() {

        // create list
        List<String> list = new ArrayList<String>();
        // add elements
        list.add("First Day");
        list.add("Second Day");
        list.add("Third Day");

        /**
         *  traversal
         */
        /** 1 */
        for (String str : list) {
            System.out.println(str);
        }

        /** 2  To Array*/
        String [] strArray = new String[list.size()];
        list.toArray(strArray); // create array

        for (int i = 0; i < strArray.length; i++) {
            System.out.println(i + " | "+strArray[i]);
        }

        /** 3 iterator */
        Iterator<String> it = list.iterator(); // iterator
        while (it.hasNext()) {
            System.out.println(it.next());
        }


    }
}


/**
 * 
 * @author Henry
 *
 * Desc: Test Map
 */
class MyMap {
    public void MyMapShow() {

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

        // add elements
        map.put("<1>", "First Day");
        map.put("<2>", "Second Day");
        map.put("<3>", "Third Day");

        /**
         * Traversal
         */
        /** 1   keyset */
        for (String  key : map.keySet()) {
            System.out.println(key+" | "+map.get(key));
        }

        /** 2  通过Map.entrySet使用iterator遍历key和value： */
        Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<String,String> entry = it.next();
            System.out.println("Key: "+entry.getKey()+" | Value: "+entry.getValue());
        }

        /** 3 通过Map.entrySet遍历key和value    ...推荐，尤其是容量大时 */
        for (Map.Entry<String, String> entry : map.entrySet()) {
            System.out.println("Key: "+entry.getKey()+" | Value: "+entry.getValue());
        }

        /** 4 通过Map.values()遍历所有的value，但不能遍历key */
        for (String str : map.values()) {
            System.out.println(str);
        }

    }
}



public class TestCollectionFramework {

    public static void main(String[] args) {

        /**
         * Test List
         */
        MyList list = new MyList();
        list.MyListShow();

        /**
         * Test Map
         */
        MyMap map = new MyMap();
        map.MyMapShow();

    }

}