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Module 4 Control Structures Conditional Statements

2026-03-05 14:13 Tags: #java Author: Duke Hsu

Key concepts

  • Conditional Statements

    Conditional statements allow a program to make decisions based on conditions. In Object-oriented programming , they are commonly used inside methods of a class to control object behavior

  • if Statement

    Executes a block of code if a condition is true

  • if-else if-else statement

    Used when checking multiple condition (more than 2 ), conditions are checked from top to bottom, once one condition is true, the rest are skipped.

  • Switch statement

    Best used when comparing one variable to multiple fixed values - Variable can be: int, char, String, enum - break prevents fall-through - default is optional but recommended

  • Nested if statement

    A nested if statement is an if statement placed inside another if statement. It is used when:

    1. A second condition must be checked only if the first condition is true.

    2. you need multiple levels of decision-making.

    3. you are validating conditions step-by- step .

  • if -else statement

    Executes one block if true, another if false

Real-Life Example

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//if statement
boolean isRaining = true;

if (isRaining){

    System.out.println("Bring an umbrella!");

}


//if-else
int weather = 1; //1= sunny, 2 = raining, 3 = cloudy

if (weather == 1){

    System.out.println("We are going to park~!");

}else {

    System.out.println("We stay home");
}




//if-else if 
int grade = 70;
if(grade >= 90){

    System.out.println("You are super smart");

} else if(grade >=80) {

    System.out.println("Very Good");

}else if(grade >=70){

    System.out.println("You are good"):
}else{

    System.out.println("You are not bobo, but u need hard learning!");
}


//netsted if 

int age == 16;

boolean haveNationalID = true;


if(age >= 18){
    System.out.println("Old enough to work~");

    if(haveNationalID){

        System.out.println("And you have national ID, You can get a job");

    }else{

        System.out.prinln("You must get national ID first !~");

    }

}else{

    System.out.println("Hey, you should go back to your home ~!");
}

Switch Statements

Instead of writing many if...elsestatements, you can use the switch statement.

Think of it like ordering food in a restaurant : if you choose A, you get pizza, if you choose B , you get a burger. otherwise , you get nothing .

The switchstatement selects one of many code blocks to be executed.

Syntax

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switch(expression){
    case x:
        //code block
        break;

    case y:
        //case y block
        break;

    default:
        //default code block 
}

Example: 

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int userChoose = 4;

switch (userChoose){
    case 1:
        System.out.println("Pizza~~");
        break;

    case 2:
        System.out.println("Burger");
        break;
    case 3:
        System.out.println("Coca cola");
        break;

    default:
        System.out.println("Service water");
}

References

Module 4 PPT