Map-读写性能对比

package lzh;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

public class TestMapForeachEntry {

public static void main(String[] args) {
// 初始化，10W次赋值
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (int i = 0; i < 100000; i++)
map.put(i, i);

/** 增强for循环，keySet迭代 */
long start = System.currentTimeMillis();
for (Integer key : map.keySet()) {
map.get(key);
}
long end = System.currentTimeMillis();
System.out.println("增强for循环，keySet迭代 -> " + (end - start) + " ms");

/** 增强for循环，entrySet迭代 */
start = System.currentTimeMillis();
for (Entry<Integer, Integer> entry : map.entrySet()) {
entry.getKey();
entry.getValue();
}
end = System.currentTimeMillis();
System.out.println("增强for循环，entrySet迭代 -> " + (end - start) + " ms");

/** 迭代器，keySet迭代 */
start = System.currentTimeMillis();
Iterator<Integer> iterator = map.keySet().iterator();
Integer key;
while (iterator.hasNext()) {
key = iterator.next();
map.get(key);
}
end = System.currentTimeMillis();
System.out.println("迭代器，keySet迭代 -> " + (end - start) + " ms");

/** 迭代器，entrySet迭代 */
start = System.currentTimeMillis();
Iterator<Map.Entry<Integer, Integer>> iterator1 = map.entrySet().iterator();
Map.Entry<Integer, Integer> entry;
while (iterator1.hasNext()) {
entry = iterator1.next();
entry.getKey();
entry.getValue();
}
end = System.currentTimeMillis();

System.out.println("迭代器，entrySet迭代 -> " + (end - start) + " ms");
}
}

/**
增强for循环，keySet迭代 -> 17 ms
增强for循环，entrySet迭代 -> 13 ms
迭代器，keySet迭代 -> 15 ms
迭代器，entrySet迭代 -> 6 ms
*/