Google Guava学习之Immutable Collection

以前为了实现传递不可变容器，我们常要做预防性拷贝，实现起来很繁琐。

Guava的Immutable Collection实现了只读容器。当你试图调用改变容器的操作时，就会有相应的异常抛出。

以下代码以ImmutableMap和ImmutableSet做为例子。

import java.util.HashMap;
import java.util.Map;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.ImmutableSortedSet;

public class TryImmutableMap {
public static void main(String[] args) {
Map<String, String> map = new HashMap<String, String>();
map.put("abc", "def");
map.put("def", "efg");
// a immutable map is cloned from a regular map.
ImmutableMap<String, String> aImmutalbeMap = ImmutableSortedMap.<String, String>copyOf(map);
//aImmutalbeMap.put("tgh", "ihg"); // Exception!! You can't change it.
//aImmutalbeMap.clear();			// Exception!! You can't change it.
//aImmutalbeMap.remove("abc");		// Exception!! You can't change it.
System.out.println(aImmutalbeMap.containsKey("abc")); // this line is ok.
// for immutable set
ImmutableSet<String> immutableSet = ImmutableSortedSet.<String>of("abc", "def", "efg");
System.out.println(immutableSet); // output: [abc, def, efg]
// for small immutable map
ImmutableMap<String, String> immutableMap = ImmutableSortedMap.<String, String>of("abc", "def");
System.out.println(immutableMap); // output: {abc=def}
}
}