Java If Statement
In this chapter you will learn:
- Learn the simplest form of if statement
- How to the if/else statement
- How to use the nested if statements
- Learn how to use the if-else-if Ladder
Basic If Statement
The following the simplest form of Java if statement:
if(condition)
statement;
condition is a boolean expression. If condition is true,
then the statement is executed. If condition is false, then
the statement is bypassed.
Here is an example:
public class Main {
/*j a va 2 s . co m*/
public static void main(String args[]) {
int num = 99;
if (num < 100) {
System.out.println("num is less than 100");
}
}
}
The output generated by this program is shown here:
If statement is often used to to compare two variables. The following code defines two variables,
x and y, the it uses the if statement to compare them and prints out messages.
public class Main {
// j a va2 s. c o m
public static void main(String args[]) {
int x, y;
x = 10;
y = 20;
if (x < y){
System.out.println("x is less than y");
}
x = x * 2;
if (x == y){
System.out.println("x now equal to y");
}
x = x * 2;
if (x > y){
System.out.println("x now greater than y");
}
if (x == y){
System.out.println("===");
}
}
}
The output generated by this program is shown here:
We can also use a boolean value to control the if statement. The value of a boolean variable
is sufficient, by itself, to control the if statement.
public class Main {
public static void main(String args[]) {
boolean b;/*from jav a 2 s . c o m*/
b = false;
if (b) {
System.out.println("This is executed.");
} else {
System.out.println("This is NOT executed.");
}
}
}
There is no need to write an if statement like this:
if(b == true) ...
The output generated by this program is shown here:
If else statement
The if statement is a conditional branch statement.
Here is the general form of the if-else statement:
if (condition)
statement1;
else
statement2;
The else clause is optional. Each statement may be a single statement or a compound
statement enclosed in curly braces (a block). Only one statement can appear directly after the if or the else.
To include more statements, you'll need to create a block, as in this fragment:
public class Main {
public static void main(String[] argv) {
int i = 1;//j av a 2 s.co m
if (i > 0) {
System.out.println("Here");
i -= 1;
} else
System.out.println("There");
}
}
]]>
The output:
It is clear to include the curly braces when using the if statement,
even when there is only one statement in each clause.
Nested if statements
A nested if is an if statement inside another another if
statement or else. The following code uses a nested if statement to compare values.
public class Main {
public static void main(String[] argv) {
int i = 10;/*from j a va 2 s .c om*/
int j = 4;
int k = 200;
int a = 3;
int b = 5;
int c = 0;
int d =0;
if (i == 10) {
if (j < 20){
a = b;
}
if (k > 100){
c = d;
}
else{
a = c;
}
} else{
a = d;
}
System.out.println("a = " + a);
System.out.println("b = " + b);
System.out.println("c = " + c);
System.out.println("d = " + d);
}
}
The output:
The if-else-if Ladder
The if-else-if Ladder looks like this:
if(condition) /*java2 s. com*/
statement;
else if(condition)
statement;
else if(condition)
statement;
.
.
else
statement;
Here is a program that uses an if-else-if ladder.
public class Main {
public static void main(String args[]) {
int month = 4;
String value;/* jav a2s. c o m*/
if (month == 1 )
value = "A";
else if (month == 2)
value = "B";
else if (month == 3)
value = "C";
else if (month == 4)
value = "D";
else
value = "Error";
System.out.println("value = " + value);
}
}
Here is the output produced by the program:
Next chapter...
What you will learn in the next chapter:
- What is the Java Switch Statement Syntax
- How to use the optional break statement
- How to write nested switch Statements