Bargains With Evil
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(→Lawyer Up To Read Other Contracts) |
(→Read The Contract Carefully!) |
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| − | Betimes we must bargain with others, even with evil. In Java, these bargains are made with | + | Betimes we must bargain with others, even with evil. In Java, these bargains are made with a fearsome form of contract, the '''method call'''. Method calls have '''arguments''' and '''return values'''. The arguments are what you give, and the return value is what you receive in exchange. |
==(A) Striking A Bargain== | ==(A) Striking A Bargain== | ||
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== Read The Contract Carefully!== | == Read The Contract Carefully!== | ||
| − | The first thing we must understand in these code examples is the idea of '''local variables'''. Local variables are declared within | + | The first thing we must understand in these code examples is the idea of '''local variables'''. Local variables are declared within methods. Local variables can ONLY be used inside their own methods, and actually only within their own block and any inner blocks. This is a principle called '''scope'''. Arguments in method signatures are also local variables. |
| − | A method call sets argument variables in the method. In the Innocent.main() call to Evil.bargain(), Evil.bargain()'s whatIsGiven argument is set to the String "honor". Methods can return a single value, which can be placed in a variable, used, or ignored. Evil.bargain() returns a | + | (The variables we have seen declared outside of methods are called ''fields''. Fields can be used in any method. If they are ''public'', then any method of any class can use them. If they are ''private'', then only methods of their own class can use them. Demons do have secrets to keep, after all.) |
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| + | A method call sets argument variables in the method. In the Innocent.main() call to Evil.bargain(), Evil.bargain()'s whatIsGiven argument is set to the String "honor". | ||
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| + | Methods can return a single value, which can be placed in a variable, used, or ignored. A method returns a value using the '''return''' reserved word, as you see at the end of both methods of Evil. If the return type of a method is '''void''', no value is returned and there is no need for a return statement. Evil.bargain() returns a String with the value "despair" to Innocent.main(), which places that value into the String named 'result'. | ||
Arguments and returns can be any types or combination of types. | Arguments and returns can be any types or combination of types. | ||
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==Create Your Own Contracts== | ==Create Your Own Contracts== | ||
# Add a method to Evil that has int[] as an argument which returns the sum of the first three elements in the array. | # Add a method to Evil that has int[] as an argument which returns the sum of the first three elements in the array. | ||
| − | # In Innocent.main(), create a local variable array with at least 3 elements | + | # In Innocent.main(), create a local variable array with at least 3 initialized elements (curly braces!) |
# Add a call to your new Evil method using the array for the argument. Print the result. | # Add a call to your new Evil method using the array for the argument. Print the result. | ||
