java list三种遍历方法性能比较

Posted 2020-09-22 腾逸

public static void compare() {
    List<String> list = new ArrayList<String>();
    Set<String> set = new HashSet<String>();
    for(int i=0;i<100000;i++) {
        list.add("a"+i);
    }
    long t1=0L,t2=0L;
    t1 = System.currentTimeMillis();
    for(String s : list) {
        set.add(s);
    }
    t2 = System.currentTimeMillis();
    System.out.println("forEach遍历的时间为："+(t2-t1)+"mm");
    ////two
    t1 = System.currentTimeMillis();
    for(int i=0; i<list.size(); i++) {
        String str = list.get(i);
        set.add(list.get(i));
    }
    t2 = System.currentTimeMillis();
    System.out.println("size遍历的时间为："+(t2-t1)+"mm");
    ////three
    t1 = System.currentTimeMillis();
    Iterator<String> iterator = list.iterator();
    while(iterator.hasNext()) {
        String str = iterator.next();
        set.add((String)iterator.next());
    }
    t2 = System.currentTimeMillis();
    System.out.println("iterator遍历的时间为："+(t2-t1)+"mm");
}

forEach遍历的时间为：45mm
size遍历的时间为：14mm
iterator遍历的时间为：7mm