java畢業(yè)設(shè)計外文文獻(xiàn)原文及譯文-wenkub
2022-12-04 03:19:19 本頁面
【正文】 you’re manipulating is the reference, which in turn modifies the object. If you want to move around the room and still control the television, you take the remote/reference with you, not the television. Also, the remote control can stand on its own, with no television. That is, just because you have a reference doesn’t mean there’s necessarily an object connected to it. So if you want to hold a word or sentence, you create a String reference: But here you’ve created only the reference, not an object. If you decided to send a message to s at this point, you’ll get an error (at run time) because s isn’t actually attached to anything (there’s no television). A safer practice, then, is always to initialize a reference when you create it. 第 3 頁 共 7 頁 However, this uses a special Java feature: strings can be initialized with quoted text. Normally, you must use a more general type of initialization for objects When you create a reference, you want to connect it with a new object. You do so, in general, with the new keyword. The keyword new says, “Make me a new one of these objects.” So in the preceding example, you can say: Not only does this mean “Make me a new String,” but it also gives information about how to make the String by supplying an initial character string. Of course, String is not the only type that exists. Java es with a plethora of readymade types. What’s more important is that you can create your own types. In fact, that’s the fundamental activity in Java programming, and it’s what you’ll be learning about in the rest of this book It’s useful to visualize some aspects of how things are laid out while the program is running—in particular how memory is arranged. There are six different places to store data: Registers. This is the fastest storage because it exists in a place different from that of other storage: inside the processor. However, the number of registers is severely limited, so registers are allocated by the piler according to its needs. You don’t have direct control, nor do you see any evidence in your programs that registers even exist. The stack. This lives in the general randomaccess memory (RAM) area, but
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