If the reference values of obj and this are equal There are a couple ways to approach this, but best practice suggests a multi-step “filtering” approach that first weeds out special cases Way Implementation equals, hashCode ,and toString equals, hashCode, and toString should all behave in ways that depend on these abstract mathematical model values.which means the equal method compare reference value, maybe its not what the developer wants to compare with.Object cannot possibly know anything about the abstract mathematical model values (i.e., the object values) of variables.Object cannot possibly know anything about the abstract mathematical model values (i.e., the object values) of variables The Crux of the Problem Default implementation of toString: “returns a string consisting of the name of the class of which the object is an instance, the at-sign character and the unsigned hexadecimal representation of the hash code of the object.”.“typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.Default implementation of equals: “for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x = y has the value true).”.Object class method Common Method from ObjectĮevery Java class implicitly extends the class Object, which defines the following methods and provides default implementations that you should override:ĭefault implmentation of equals, hashCode ,and toString Another level of access control between public and private.A namespace: units in different packages may have the same name without conflict.– Logical structuring: packages are hierarchical, i.e., you may have packages within packages.– Example: the Queue-family components are all in the package components.queue Declared types literally “disappear” in the JVMĮach OSU CSE component family is bundled into its own package, i.e., a grouping of interfaces and classes that the designer thinks “belong together” for logical reasons.– Once a Java program compiles, only object types are kept at run-time.If the declared type is an interface type, then the object type (a class) must implement the declared type (an interface.The object type can never be an interface type, because you may not instantiate a variable using new followed by an interface type.The declared type of a variable may be an interface type.Recall the rules for declared types and object (dynamic) types.– Used by the Java compiler for type-checking with declared types: to make sure variables are used only where they make sense.An interface type may be used in Java even if there is no implementation of it in scope.Java interface define as type, i.e., the type name along with the set of its instance methods.Most powerful interface Notice there is Circularity Check every kernel method’s precondition.Determine the value of a variable of the type. ![]() Give a variable of the type any allowable value.A minimal set of methods that is functionally complete, i.e., powerful enough to:.The enhanced interface defines contracts for all other methods for the type.– Contract(s) for methods inherited from Java library interfaces that do not have their own contract specifications (if applicable e.g., an iterator or a comparator).it is unusual for an interface to define variables.Final Review Java Interface Interface may be used to define:
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