Java Escape Quotes

Once an object escapes, you have to assume that another class or thread may, maliciously or carelessly, misuse it. This is a compelling reason to use encapsulation: it makes it practical to analyze programs for correctness and harder to violate design constraints accidentally.

Modernism was based on a kind of arrogance ... and led designers to believe that if they thought of something cool, it must be considered universally cool. That is, if something's worth doing, it's worth driving into the ground to the exclusion of all other approaches. Look at the use of parentheses in Lisp or the use of white space as syntax in Python. Or the mandatory use of objects in many languages, including Java. All of these are ways of taking freedom away from the end user "for their own good". They're just versions of Orwell's Newspeak, in which it's impossible to think bad thoughts. We escaped from the fashion police in the 1970s, but many programmers are still slaves of the cyber police.

Publishing an object means making it available to code outside of its current scope, such as by storing a reference to it where other code can find it, returning it from a nonprivate method, or passing it to a method in another class. In many situations, we want to ensure that objects and their internals are not published. In other situations, we do want to publish an object for general use, but doing so in a thread-safe manner may require synchronization. Publishing internal state variables can compromise encapsulation and make it more difficult to preserve invariants; publishing objects before they are fully constructed can compromise thread safety. An object that is published when it should not have been is said to have escaped. Section 3.5 covers idioms for safe publication; right now, we look at how an object can escape. The

A common mistake that can let the this reference escape during construction is to start a thread from a constructor. When an object creates a thread from its constructor, it almost always shares its this reference with the new thread, either explicitly (by passing it to the constructor) or implicitly (because the Thread or Runnable is an inner class of the owning object). The new thread might then be able to see the owning object before it is fully constructed. There's nothing wrong with creating a thread in a constructor, but it is best not to start the thread immediately. Instead, expose a start or initialize method that starts the owned thread. (See Chapter 7 for more on service lifecycle issues.) Calling an overrideable instance method (one that is neither private nor final) from the constructor can also allow the this reference to escape. If

An object is immutable if: Its state cannot be modifled after construction; All its flelds are final;[12] and [12] It is technically possible to have an immutable object without all fields being final—String is such a class—but this relies on delicate reasoning about benign data races that requires a deep understanding of the Java Memory Model. (For the curious: String lazily computes the hash code the first time hashCode is called and caches it in a nonfinal field, but this works only because that field can take on only one nondefault value that is the same every time it is computed because it is derived deterministically from immutable state. Don't try this at home.) It is properly constructed (the this reference does not escape during construction).

Do not allow the this reference to escape during construction.

Beyond the deprivations, degradations, and tortures these prisoners endured, each man often recounts how he got to the camps Weller visited. These conflicts, and all they implied, would have been instantly recognizable to the 1945 public. Many of the Dutch and the British, the Australians and Canadians, were taken in the defeats of Singapore (130,000), Java (32,000), and Hong Kong (14,000). Many of the Americans got captured on Guam or Wake; or in the Philippines (75,000), to then endure the Bataan death march, on which one in four died. Some built the Siam-Burma railroad, which claimed yet another 15,000 lives, same ratio. Nearly everywhere, in a hurry, the Japanese won and the Allies lost. The United States saw its navy smashed at Pearl Harbor and its Pacific air forces wiped out in Manila, just before MacArthur got himself safely out to Australia. This litany of early military disasters added up to astonishing numbers. In a mere six months the Japanese, at a cost of only 15,000 of their own men (deaths and casualties), took 320,000 Allied soldiers out of the war, either as deaths, casualties, or prisoners; over half these were Asiatic. White prisoners, about 140,000 total over the course of the conflict, became slave labor across the growing Japanese empire. (Asiatic prisoners were often turned loose, as good propaganda among the subjugated peoples.) Japan had not signed the 1929 Geneva Conventions regarding treatment of prisoners of war, and a Japanese soldier would sooner be killed than captured: thus every enemy soldier who surrendered was a coward, a cur, a thing. Any notion of “inhumane treatment” toward a surrendered Chinese, much less a white man, was incomprehensible. White men were the foe, so their role was to work, then die. Whether their deaths proved painful did not matter to the Japanese. Unlike the Nazi POW camps, there were few escape attempts, for it was obvious to any Allied POW in Asia that a white face was an immediate giveaway even had he succeeded, and the Japanese made it clear that they would execute ten men for every man who escaped. Statistically it was seven times healthier to be a POW under the Nazis than under the Japanese. By war’s end, one out of every three white prisoners had died as their captives—“starved to death, worked to death, beaten to death, dead of loathsome epidemic diseases that the Japanese would not treat,” as Daws puts it. Another year of war and there would have been no POWs still alive. (A Japan War Ministry directive of August 1944 iterated that “the aim is to annihilate them all, and not to leave any traces.”)