1 ArrayList HashSet HashMap are all thread-unsafe. The following methods are used to achieve thread-safety when multiple threads access these classes at the same time
/**
* Use Collections to manage sync containers
ArrayList HashSet HashMap are all thread-unsafe. The following methods are used to achieve thread-safety when multiple threads access these classes at the same time.
* synchronizedList()
synchronizedSet()
synchronizedMap()
* @author Administrator
*
*/
public class Demo01 {
/**
* @param args
*/
public static void main(String[] args) {
List<String> list =new ArrayList<String>();
list.add("a");
list.add("b");
//list can be synchronized
List<String> synList =Collections.synchronizedList(list);
System.out.println("The thread-safe list is made");
}
}
2 Read-only settings:
/**
* read only settings
* emptyXxx() empty immutable collection
* 1、emptyList()
* emptyMap()
* emptySet()
2. singletonXxx() an immutable set of elements
singleton(T o)
singletonList(T o)
singletonMap(K key, V value)
3. unmodifiableXxx() immutable container
unmodifiableList(List<? extends T> list)
unmodifiableSet(Set<? extends T> s)
unmodifiableMap(Map<? extends K,? extends V> m)
* @author Administrator
*
*/
public class Demo02 {
/**
* @param args
*/
public static void main(String[] args) {
Map<String,String> map =new HashMap<String,String>();
map.put("test", "test");
map.put("bjsxt", "bjsxt");
// read only control
Map<String,String> map2 =Collections.unmodifiableMap(map); // Control this container can no longer be modified
//map2.put("a", "a"); //Cannot operate
System.out.println(map2.size());
// container test for an element
List<String> list =Collections.singletonList(new String()); // container with only one element
list.add("test");
//list.add("bjsxt"); //Container that can only contain one element
}
public static Set<String> oper(Set<String> set){
if(null==set){
return Collections.EMPTY_SET; //External acquisition to avoid NullPointerException
}
//operate
return set;
}
}