tailieunhanh - Java All-in-One Desk Reference For Dummies phần 4

Một nhà điều hành hợp lý (đôi khi được gọi là một nhà điều hành boolean) là một nhà điều hành mà trả về một kết quả boolean đó là dựa vào kết quả boolean Các nhà khai thác của ông Spock yêu thích (logic nhất, khóa học) Không có Hình 4-3: Các sơ đồ cho một chuỗi các khác nếu báo cáo. | Understanding Objects 241 Attribute Object 1 Object 2 Number One Two Color Red Blue The type of an object determines what attributes the object has. Thus all objects of a particular type have the same attributes. However they don t necessarily have the same values for those attributes. In this example all Fish have attributes named Number and Color but the two Fish objects have different values for these attributes. The combination of the values for all the attributes of an object is called the object s state. Unlike its identity an object s state can and usually does change over its lifetime. For example some fish can change colors. The total sales for a customer changes each time the customer buys another product. The grade point average for a student changes each time a new class grade is recorded. And the address and phone number of an employee changes if the employee moves. Here are a few more interesting details about object state Some of the attributes of an object are publicly known but others can be private. The private attributes may be vital to the internal operation of the object but no one outside of the object knows they exist. They re like your private thoughts They affect what you say and do but nobody knows them but you. In Java the state of an object is represented by class variables which are called fields. A public field is a field that s declared with the public keyword so the variable can be visible to the outside world. Objects have behavior Another characteristic of objects is that they have behavior which means they can do things. Like state the specific behavior of an object depends on its type. But unlike state the behavior isn t different for each instance of a type. For example suppose all the students in a classroom have calculators of the same type. Ask them all to pull out the calculators and add two numbers any two numbers of their choosing. All the calculators display a different number but they all add the same. In other words .

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