{"id":2485,"date":"2023-12-20T13:05:08","date_gmt":"2023-12-20T12:05:08","guid":{"rendered":"https:\/\/oopm.org\/?page_id=2485"},"modified":"2024-12-15T09:26:27","modified_gmt":"2024-12-15T08:26:27","slug":"4c-3-parameter-transfer","status":"publish","type":"page","link":"https:\/\/oopm.org\/?page_id=2485","title":{"rendered":"7.3 Parameter transfer and return value"},"content":{"rendered":"
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For a class instantiation, an object is created and for a method invocation, a method object is created.<\/p>\n\n\n\n

Then the actual parameters of the invocation\/instantiation are evaluated and transferred to the corresponding data-items of the method object\/object. When the method has been executed, a possible value may be returned.<\/p>\n\n\n\n

Parameter transfer<\/h2>\n\n\n\n

The transfer of parameters corresponds to assignment of the actual parameters to the formal parameters. Consider the following method invocation:<\/p>\n\n\n\n

 transfer(account_1010,account_1022, 218)<\/code><\/pre>\n\n\n\n
The invocation consists of the following steps:<\/p>\n\n\n\n
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  1. A transfer<\/code>-object is generated – assume that aTransfer<\/code> refers to this object. The situation is then as shown in the snapshot where the reference variables from<\/code> and to <\/code>have the initial value none<\/code> and amount<\/code> has the initial value 0 (zero).<\/li>\n<\/ol>\n<\/div>\n\n\n\n
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    \"\"<\/figure>\n<\/div>\n<\/div>\n\n\n\n
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    2. The actual parameters are then assigned to the corresponding data-items in aTransfer<\/code>:<\/p>\n\n\n\n
    aTransfer.from := account_1010aTransfer.to := account_1022<\/code>aTransfer.amount := 218<\/code><\/code><\/pre>\n\n\n\n
    The situation is then as shown in the snapshot where the from<\/code> refers to account_1010<\/code>, to<\/code> refers to account_1022<\/code>, and amount<\/code> has the value 218.<\/p>\n<\/div>\n\n\n\n
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    \"\"<\/figure>\n<\/div>\n<\/div>\n\n\n\n
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    3. The statements of aTransfer<\/code> are executed:<\/p>\n\n\n\n
    from.withdraw(amount)\nto.deposit(amount)<\/code><\/pre>\n\n\n\n
    The situation is then as shown in the snapshot.<\/p>\n<\/div>\n\n\n\n
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    \"\"<\/figure>\n<\/div>\n<\/div>\n\n\n\n
    In the example, we have two types of parameters:<\/p>\n\n\n\n
    Amount<\/code> is a a value parameter<\/em> of type integer. A value type is copied to the data-item of the method object.<\/p>\n\n\n\n
    From<\/code> and to<\/code> are reference parameters<\/code>. For a reference parameter the reference is assigned to the data-item in the method object.<\/p>\n\n\n\n
    For an elaboration of the difference between value and object and thus value assign and reference assign, see section