The difference and contact between the For loop and the Foreach loop during traversal

1, the For loop and the Foreach Loop function can traverse a list, such as

for (int i = 0; i < list.size; i + +) {
    
} for
(int i = list.size (); i > 0; I-) {
    
} for
(Class C:lis T) {
}

2, however, the following case for + + and for--not universal (when the base of the loop changes, for example, the following example, two times per loop inserts an object)

Can do this

for (int i = t.size (); i > 0; I-) {
	if (i% 2 = = 0)
	  t.add (New Test ());
}

But you can't do that.

for (int i = 0; i < t.size (); i + +) {
	if (i 2 = = 0)
	  t.add (New Test ());
}

This is because, in the process of add, the value of T.size () is constantly changing, so this cardinality change can only be used--

3. For the difference between the for and foreach, the relationship of time complexity, foreach is in the constant new object out, such as the following

Package demo_20141031;

Import java.util.ArrayList;
Import java.util.Date;
Import java.util.List;

public class Test {
	private String name = "";
	
	
Public	String GetName () {
//		return name;	} public
	void SetName (String name) {
		this.name = name;
	}
	/**
	 * @param args
	 *
	/public static void main (string[] args) {
		//TODO auto-generated method stub
  
   list<test> t = new arraylist<test> ();
		Test temp = new test ();
		String a = "n";
		String B = "1";
		for (int i = 0; i <; i + +) {
			temp.setname (a);
			T.add (temp);
		}
		
		System.out.println ();		Long TIME0 = new Date (). GetTime ();
for		(int i = 0; i < t.size (); i + +) {
////		}
		Long time1 = new Date (). GetTime ();
		for (Test temps:t) {
			
		}
		long time2 = new Date (). GetTime ();		System.out.println (TIME1-TIME0);
		System.out.println (time2-time1);
	}
}