Decision Trees

Key Ideas

If Statements Switch Statements String Functions

Readings

https://books.trinket.io/thinkjava2/chapter5.html

https://www.geeksforgeeks.org/decision-making-javaif-else-switch-break-continue-jump/?ref=lbp

Observations

Definition

The is statement has the following form:

if(condition){

}

        if(condition)
        {
    		// runs if true
        }
    
        if(condition)
        {
    		// code here runs if true
        }
        else
        {
    		// code here runs if false
        }
    
        if(condition)
        {
    		// code here runs if true
        }
        else if(condition)
        {
    		// code here runs if true
        }
        else if(condition)
        {
    		// code here runs if true
        }
        else
        {
    		// code here runs if false
    		// the else is optional
        }
    

Warning

In order to compare Strings, you must use .equal(argument)

String string1 = "aaa";
String string2 = "bbb";

if (string1.equals(string2))
{
    // Do something
}

Tip

Note in the code below how a string is converted to an integer - Integer.parseInt() and to a double Double.parseDouble()

Lecture Code

//James Goudy
//If demo


import java.util.Scanner;

public class If_Demo {

    static void if_one(double num) {
        
        //Example is checking for true only
        System.out.println("Example 1  \n");

        if (num < 100) {
            System.out.println(num + " is less than 100 \n");
        }

    }

    static void if_two(double num) {
        
        //This example is checking for both true and false
        System.out.println("Example 2  \n");

        if (num < 100) {
            System.out.println(num + " is less than 100 \n");
        } else {
            System.out.println(num + " is greater than 100 \n");
        }

    }

    static void if_three(double num) {
        
        //This example is an  example of an else if statement
        System.out.println("Example 3  \n");

        if (num < 10) {
            System.out.println(num + " is less than 10 \n");
        } else if (num < 20) {
            System.out.println(num + " is less than 20 \n");
        } else if (num <= 30) {
            System.out.println(num + " is less than 30 \n");

        } else {
            System.out.println(num + " is greater than 30 \n");
        }

    }

    static void if_range(double salary) {
        
        //check to see if a number is within a range of numbers
        System.out.println("Example Range of Numbers  \n");
        
        if (salary > 0 && salary <= 50000) {
            System.out.println(" You are poor \n");
        } else if (salary > 50000 && salary <= 200000) {
            System.out.println(" You are middle class \n");
        } else {
            System.out.println(" You are rich \n");
        }

    }

    static void if_string(String vehicle) {
        //you should always convert your comparasion to 
        //a consistent state.  Comparisons for strings are
        //case sensitive.

        vehicle = vehicle.toLowerCase();

        //String is an object so Java requres 
        //the  .equals to compare the equality of 
        //strings.  In other language you may
        // be able to use the  ==
        
        if (vehicle.equals("boat")) {
            System.out.println("You are a boater \n");

        } else if (vehicle.equals("car")) {
            System.out.println("You are a driver \n");
        } else if (vehicle.equals("plane")) {
            System.out.println("You are a pilot \n");
        } else {
            System.out.println("That wasn't a choice \n");
        }

    }

    public static void main(String[] args) {

        //variables
        double num1 = 0;
        double mySalary = 0;
        String myVehicle;

        //create scanner
        Scanner sc1 = new Scanner(System.in);

        //input number
        System.out.println("Enter a number");
        num1 = Integer.ParseInt(sc1.nextLine());

        //if example one
        // if the number is less than 100 the message will appear
        System.out.println("If Example - checking for true only\n");
        if_one(num1);

        //if example two
        //this example for both a true and false condition
        System.out.println("If Example Two - " 
                            + "checking for a both true and false\n");
        if_two(num1);

        //if example three
        //this example an else if example
        System.out.println("Else if example - "
                            + "checking for multiple conditions \n");
        if_three(num1);

        //if example - check for a number within a range
        System.out.println("Checkin to see if a number is within a range\n");
        System.out.println("Enter your salary\n");
        mySalary = Double.ParseDouble(sc1.nextLine());
        if_range(mySalary);

        //An example using a string
        System.out.println("This is an example of comparing strings \n");
        System.out.println("Please enter your favorite "
                            + "vehicle - boat, car, plane \n");     
        sc1.nextLine(); 
              
        myVehicle = sc1.nextLine();
        if_string(myVehicle);
      
        //exit program
        System.out.println("Press enter to exit \n");
        sc1.nextLine();
        
    }

}

In Class

Post This Exercise

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End Of Topic