A Quick and Dirty Overview of Java and Java Programming

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$Syllabus for CS/MATH 278 Discrete Mathematics for Computer ...$

.Each new instruction performs a certain task, it has a name (the name of the method), it iscapable of receiving some inputs and producing one result.Input ParametersLet us start by making some observations regarding the parameters of a method. Parametersare employed to provide an input to the method at the time of its execution. Each time amethod is executed, different inputs can be provided.Let us start by looking at the following simple exampleimport java.io.*;public class testMethod{// this is a method that attempts to swap the value of two variablespublic static void swap (int x, int y){int temp;}temp = x;x = y;y = temp;// this is a main program to test the method abovepublic static void main (String args[]){int a=2;int b=9;}}System.out.println(“Before swap: a=”+a+” b=”+b);swap(a,b);System.out.println(“After swap: a=”+a+” b=”+b);The result of executing the program is:Before swap: a=2 b=9After swap: a=2 b=9So, it appears that the two variables did not get swapped by the swap method. Why?? Thiseffect derives from the particular methodology that Java uses to communicate the inputs to amethod upon call. Let us see what really happens when we perform a call to a method. Whenthe method main is started, its local variables are created and its execution starts; the memoryconfiguration is as follows:22
int a=2;int b=9;System.out…swap(a,b);….MEMORY29abWhen we perform a call to a method, the following steps are taken:• first of all, the expressions that are specified as actual parameters in the method callare completely evaluated. Each actual parameter in the call should ultimately reduceto a single element. For example, if we consider the following call to the methodsqrt:Math.sqrt(12*x+5)The actual parameter in this method call is the expression 12*x+5; when the methodis called, the system will first compute the value of this expression.• Next, the method is started; upon starting the method, all the local variables of themethod are created; in particular, the formal parameters of the method are treatedjust as any other local variables, and thus they are created as new variables when themethod is started. Let us consider the example above. When we call the methodswap, then all its local variables, including the formal parameters, are created. Thememory configuration when the call starts is as follows:MEMORYint a=2;int b=9;System.out…swap(a,b);….29abxtempypublic static void swap(int x, int y){int temp;…..}• once all the local variables of the method are created, the values of the actualparameters (computed in the first step) are copied in the newly created formalparameter variables. In our example, the values of the actual parameters (a,b) are 2,5;23
Page 1 and 2: Department of Computer ScienceNew M
Page 3 and 4: JavaSourceProgramJavaCompilerJVMPro
Page 5 and 6: Every method is structured in two p
Page 7 and 8: 5. lifetime: this is the period of
Page 9 and 10: In this section we will focus on a
Page 11 and 12: variable name = expressionThe expre
Page 13 and 14: StatementsThe body of a method cont
Page 15 and 16: In the first case (one-way conditio
Page 17 and 18: for ( initialization ; condition ;
Page 19: • hasNextLong(): which returns tr
Page 24 and 25: .these values are copied in the new
Page 26 and 27: .ArraysIntroductionAn array is a co
Page 28 and 29: .int[] array = new int[10];array000
Page 30 and 31: .be crated before we start reading
Page 32 and 33: .Some ExamplesComputing Average Gra
Page 34 and 35: .compute the maximum value inside a
Page 36: .}}generateNumber();do{System.out.p

A Quick and Dirty Overview of Java and Java Programming

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