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In Java, two threads can communicate by accessing a shared variable (shared-memory model).
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If two threads can both modify an object, that is, they can both execute a method that assigns to a shared variable, then the modifications must be synchronized.
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This is easy - just declare the method to be synchronized!
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This means that Java will ensure that only one thread executes the method at a time.
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Suppose more than one thread can access an account:
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public class Account
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{ int bankBalance; ...
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public synchronized void CreditAcct(int amt)
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{ ... bankBalance += amt; ... }}
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