This file for practicing basic Salesforce Data Types must be saved in a new Apex Class (any name is OK). Certain lines have FIX ME!!! in their comments, these are the practice lines where you can add in the missing Apex and check the Debug logs to see if you get the expected result when you run the test method.

2-DataTypes.java

@isTest
public static TestMethod void DataTypes(){

        string text1 = 'this text';
        string text2 = 'that text';
        
        string text3 = text1 + text2;
        System.debug(text3);
        text3 = text3 + 'more text';
        System.debug(text3);
        
        string text4 = text3.toUpperCase();
        System.debug('SHOUT! ' + text4);
        
        string text5;//FIX ME!!! Turn text4 into a lower case string.
        System.debug('whisper' + text5);
        
        string text6;//FIX ME!!! Find a string method to remove whitespaces.
        System.debug('No more whitespaces: ' + text6);
        
        string text7 = text6.remove('text');
        System.debug('This is what\'s left: ');//FIX ME!!! Edit the debug output to include text7.
        
        string text8 = text7.replace('more', 'less');
        System.debug('now with less! ' + text8);
        
        string text9 = text8.repeat(2);
        System.debug('repeated twice: ' + text9);
        
        Integer number1 = text9.length();
        System.debug('how long? ' + number1);
        
        Integer number2 = text9.indexOf('this');
        System.debug('find this: ' + number2);
        
        Integer number3;//FIX ME!!! Use indexOf() to find 'that' in text9.
        System.debug('find that: ' + number3);
        
        Integer number4 = text9.LastIndexOf('that');
        System.assertEquals(16, number4, 'Expected value should equal actual value returned by lastIndexOf()');
        
        Integer number5 = text9.IndexOf('less');
        System.assertEquals(null,null);//FIX ME!! Replace nulls with the expected index and the actual number5 result
        
        //define some numbers we'll use to work with Integers and operators
        Integer number6 = 6;
        Integer number7 = 7;
        
        Integer sum1 = number6 + number7;
        System.Debug('do the math: ' + sum1);
        System.Debug('x++ returns value then increments: ' + sum1++);
        System.Debug('what is the value now?: ' + sum1);
        System.Debug('++x increments then returns value: ' + ++sum1); 
        System.assertEquals(15, sum1);
        

        Integer sum2;//FIX ME!!! add number7 to number6
        Integer sum3;//FIX ME!!! set sum3 to increment sum2.
        //System.assertEquals(, sum3);//FIX ME!!! Uncomment and add your expected result.
        
        //What happens if we assign a non-integer value?
        Integer decimal0 = number6 / number7;
        System.debug('Integer of 2 integers divided: ' + decimal0);
        
        //Even though the result is a decimal, 2 Integers divided are still treated as integers.
        Decimal decimal1 = number6 / number7;
        System.debug('Decimal of 2 integers divided: ' + decimal1);
        
        //"Casting" is a useful technique to convert one data type to another.
        Decimal decimal2 = (decimal)number6 / (decimal)number7;
        System.debug('2 integers "cast" to decimals: ' + decimal2);
        
        //Care must be taken when working with different numeric types:
        //Explicitly declare Double or Decimal values by adding .0 if no fractional value is present
        Double nope = 5/3;
        System.debug('Double of divided integers: 5/3 != ' + nope);
        Double better = 5.0/3.0;
        System.debug('Double of divided integers with .0 added: 5.0/3.0 == ' + better);
        //Explicitly declare Long values by adding L if the number is likely to exceed 2147483647
        Long wrong = 2147483647 + 1;
        System.debug('Maximum integer value of 2147483647 plus 1: ' + wrong);
        Long right = 2147483647L + 1;
        System.debug('Maximum integer value as a Long plus 1: ' + right);
        
        //Dates and times are both tricky and easy to work with.
        Date date1 = Date.today();
        Datetime datetime1 = Datetime.now();
        Time time1 = Time.newInstance(18, 30, 2, 20);
        Time time2 = Datetime.now().time();
        Date date2 = date1 + 1;
        System.debug('Tomorrow: ' + date2);
        System.debug('Yesterday: ');//FIX ME!!! 
    }