if else statement in java
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The if statement is the most basic of all the control flow statements. It tells your program to execute a certain section of code only if a particular test evaluates to true.
Below is the structure of if statement:
if (condition) {
// Do something here if 'condition' is true.
}
The above image illustrates the flow of application when it meets a if statement.
- The program checks the condition.
- If the condition is true, code in the if block will be executed. It then continues executing the codes below the if block.
- If the condition is false, the program will ignores the code in the if block and execute code snippets below the if block.
Example:
IfExample.java
package org.o7planning.tutorial.javabasic.controlflow;
public class IfExample {
public static void main(String[] args) {
// Declare a variable, representing your age
int age = 30;
System.out.println("Your age: " + age);
// The condition to test is 'age> 20'
if (age > 20) {
System.out.println("Okey!");
System.out.println("Age is greater than 20");
}
// The code after the 'if' block.
System.out.println("Done!");
}
}
Run the example:
Your age: 30
Okey!
Age is greater than 20
Done!
The if-else statement also tests the condition. It executes the if block if condition is true otherwise else block is executed.
** if - else **
if( condition ) {
// Do something here
}
// Else
else {
// Do something here
}
Example:
IfElseExample.java
package org.o7planning.tutorial.javabasic.controlflow;
public class IfElseExample {
public static void main(String[] args) {
// Declare a variable, representing your age
int age = 15;
System.out.println("Your age: " + age);
// The condition to test is 'age> 18'
if (age >= 18) {
System.out.println("Okey!");
System.out.println("You are accepted!");
} else {
System.out.println("Sorry!");
System.out.println("Age is less than 18");
}
// The code after the 'if' block and 'else' block.
System.out.println("Done!");
}
}
Running the example:
Your age: 15
Sorry!
Age is less than 18
Done!
The structure of an if - else if - else statement is:
if(condition 1) {
// Do something here
} else if(condition 2) {
// Do something here
} else if(condition 3) {
// Do something here
}
// Else
else {
// Do something here
}
Create ElseIfExample1 class:
ElseIfExample1.java
package org.o7planning.tutorial.javabasic.controlflow;
public class ElseIfExample1 {
public static void main(String[] args) {
// Declaring a varible of type int (32 bit integer)
// Represent your test scores.
int score = 70;
System.out.println("Your score =" + score);
// If the score is less than 50
if (score < 50) {
System.out.println("You are not pass");
}
// Else if the score more than or equal to 50 and less than 80.
else if (score >= 50 && score < 80) {
System.out.println("You are pass");
}
// Remaining cases (that is greater than or equal to 80)
else {
System.out.println("You are pass, good student!");
}
}
}
Results of running the class ElseIfExample1:
Your score =70
You are pass
Change the value of the variable "score" in the above example and rerun the ElseIfExample1 class:
int score = 20;
Your score =20
You are not pass
boolean is a data type, it only has two values true or false.
Create class BooleanExample:
BooleanExample.java
package org.o7planning.tutorial.javabasic.controlflow;
public class BooleanExample {
public static void main(String[] args) {
// Declare a variable of type boolean
boolean value = true;
// If value is true
if (value == true) {
System.out.println("It's true");
}
// Else
else {
System.out.println("It's false");
}
if (value) {
System.out.println("It's true");
}
// Else
else {
System.out.println("It's false");
}
}
}
It's true
It's true
This is a list of operators, commonly used in conditional expressions.
- > Greater Than
- < Less Than
- >= Greater Than or Equal To
- <= Less Than or Equal To
- && AND
- || OR
- == HAS A VALUE OF
- != Not Equal To
- ! NOT
Example:
ElseIfExample2.java
package org.o7planning.tutorial.javabasic.controlflow;
public class ElseIfExample2 {
public static void main(String[] args) {
// Declare a variable of type int, represents your age.
int age = 20;
// Test if age less than or equal 17
if (age <= 17) {
System.out.println("You are 17 or younger");
}
// Test age equals 18
else if (age == 18) {
System.out.println("You are 18 year old");
}
// Test if age greater than 18 and less than 40
else if (age > 18 && age < 40) {
System.out.println("You are between 19 and 39");
}
// Remaining cases (Greater than or equal to 40)
else {
// Nested if statements
// Test age not equals 50.
if (age != 50) {
System.out.println("You are not 50 year old");
}
// Negative statements
if (!(age == 50)) {
System.out.println("You are not 50 year old");
}
// If age is 60 or 70
if (age == 60 || age == 70) {
System.out.println("You are 60 or 70 year old");
}
}
}
}
Chạy ví dụ:
You are between 19 and 39
You can change the value of "age" and rerun ElseIfExample2 class and see the results
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