How to define more complex Java program
A Short Program with a variable
A variable is a memory location that may be assigned a value. The value of a variable is changeable.
The following code defines a variable and change its value by assigning a new value to it.
public class Main {
public static void main(String args[]) {
int num; // a variable called num
num = 100;/* w ww .jav a 2 s . c o m*/
System.out.println("This is num: " + num);
num = num * 2;
System.out.print("The value of num * 2 is ");
System.out.println(num);
}
}
When you run this program, you will see the following output:
The following snippet declares an integer variable called num.
Java requires that variables must be declared before they can be used.
int num; // this declares a variable called num
Following is the general form of a variable declaration:
type var-name;
In the program, the line assigns to num the value 100.
num = 100; // this assigns num the value 100
Define more than one variable with comma
To declare more than one variable of the specified type, you may use a comma-separated list of variable names.
public class Main {
public static void main(String args[]) {
int num, num2;
num = 100; // assigns num the value 100
num2 = 200;//ww w. ja v a2 s . c om
System.out.println("This is num: " + num);
System.out.println("This is num2: " + num2);
}
}
When the program is run, the following output is displayed:
Using Blocks of Code
Java can group two or more statements into blocks of code. Code block is enclosing the statements between opening and closing curly braces({}).
For example, a block can be a target for Java's if and for statements.
Consider this if statement:
public class Main {
public static void main(String args[]) {
int x, y;
x = 10;//from w ww . ja va2 s . c om
y = 20;
if (x < y) { // begin a block
x = y;
y = 0;
System.out.println("x=" + x);
System.out.println("y=" + y);
} // end of block
}
}
Here is the output of the code above:
A block of code as the target of a for loop.
public class Main {
public static void main(String args[]) {
int i, y;/*from w ww. ja va 2 s . c o m*/
y = 20;
for (i = 0; i < 10; i++) { // the target of this loop is a block
System.out.println("This is i: " + i);
System.out.println("This is y: " + y);
y = y - 1;
}
}
}
The output generated by this program is shown here:
