La differenza tra fault tolerance e fault safety in Java

Number	Key	Failing	Fault-tolerant
1	Exceptions	Any changes to the collection (such as adding, deleting, and updating the collection during a thread) are to iterate over the collection and then quickly throw a concurrent modification exception.	Fault-tolerant collections do not cause exceptions.
2.	Collection types	ArrayList and hashmap collections are examples of fast-failure iterators	CopyOnWrite and concurrent modification are examples of fault-tolerant iterators
3.	Performance and memory	Instead, it works on the actual collection. Therefore, this iterator does not require additional memory and time	It is processing a clone of the collection rather than the actual collection. Time and memory overhead
4.	Modification item	The iterator does not allow modification of the collection while iterating over it.	Fault-tolerant iterator allows for modification of the collection while iterating over it.

故障保护示例

public class FailSafeExample{
　　　public static void main(String[] args){
　　　　　　ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<String, Integer>();
　　　　　　//在映射上添加元素
　　　　　　map.put("Dell", 1);
　　　　　　map.put("IBM", 2);
　　　　　　//从映射获取迭代器
　　　　　　Iterator<String> it = map.keySet().iterator();
　　　　　　while (it.hasNext()){
　　　　　　String key = (String) it.next();
　　　　　　　　　System.out.println(key+" : "+map.get(key));
　　　　　　　　　map.put("Google", 3);
　　　　　　}
　　　}
}

输出结果

IBM :2
Dell:1

故障保护示例

public class FailFastExample{
　　　public static void main(String[] args){
　　　　　　List<Integer> list = new ArrayList<Integer>();
　　　　　　list.add(1);
　　　　　　list.add(2);
　　　　　　list.add(3);
　　　　　　//从列表中获取迭代器
　　　　　　Iterator<Integer> it = list.iterator();
　　　　　　while (it.hasNext()){
　　　　　　　　　Integer integer = (Integer) it.next();
　　　　　　　　　list.add(4);
　　　　　　}
　　　}
}

输出结果

Exception in thread "main" java.util.ConcurrentModificationException
　　　at java.util.ArrayList$Itr.checkForComodification(Unknown Source)

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