Apex : String.format Demo

StringFormatDemoController.cls

public with sharing class StringFormatDemoController {
    
    public StringFormatDemoController() {
        this.demo01();
        this.demo02();
    }
    
    private void demo01() {
        String placeholder = 'Hello {0}, {1} is cool!';
        List<String> fillers = new String[]{'Jason','Apex'};
        String formatted = String.format(placeholder, fillers);
        System.assertEquals('Hello Jason, Apex is cool!', formatted);
        System.debug('demo1 = ' + formatted);
    }
    
    private void demo02() {
        // SELECT項目
        List<String> selectFields = new List<String>();
        selectFields.add('Id');
        selectFields.add('Name');
        selectFields.add('AccountNumber');
        selectFields.add('Site');
        System.assertEquals(selectFields.size(), 4);
        // 差し込みリスト
        List<String> selectQueries = new List<String>();
        for (Integer i = 0; i < selectFields.size(); i++) {
            // {0} {1} {2} {3}
            selectQueries.add('{' + String.valueOf(i) + '}');
        }
        // Query
        String query = '';
        query += ' SELECT ';
        query += String.join(selectQueries, ',');
        query += ' FROM ';
        query += ' Account ';
        query += ' LIMIT 200 ';
        String formattedQuery = String.format(query, selectFields);
        List<Account> results = Database.query(formattedQuery);
        System.debug('demo02 = ' + formattedQuery);
    }
}