Immutable objects have many advantages, including:

• Safe for use by untrusted libraries.
• Thread-safe: can be used by many threads with no risk of race conditions.
• Doesn‘t need to support mutation, and can make time and space savings with that assumption. All immutable collection implementations are more memory-efficient than their mutable siblings (analysis)
• Can be used as a constant, with the expectation that it will remain fixed

Example

public static final ImmutableSet<String> COLOR_NAMES = ImmutableSet.of(
  "red",
  "orange",
  "yellow",
  "green",
  "blue",
  "purple");

class Foo {
  final ImmutableSet<Bar> bars;
  Foo(Set<Bar> bars) {
    this.bars = ImmutableSet.copyOf(bars); // defensive copy!
  }
}

不可变的集合，其实是保证了最重要的安全性，还有性能上的提升。

也可以对这种集合做排序，比如调用ImmutableSortedSet  这个排序是在构造函数阶段排序的。

Google Guava 学习记录《4》Immutable Set

原文：http://www.cnblogs.com/-Doraemon/p/4806701.html