• 日期
• 匿名类
• lambda
• stringBuffer stringBuilder
• 定时

日期

import java.util.Calendar;
import java.util.Date;

public class Main {
    public static void main (String[] args) {
        Date date = new Date(); // 当前日期
        System.out.println(date.toString());
        Calendar calendar = Calendar.getInstance();
        System.out.println(calendar.getTime().toString());

        int year = calendar.get(Calendar.YEAR); // 年
        int month = calendar.get(Calendar.MONTH) + 1; // 月
        int cdate = calendar.get(Calendar.DATE); // 日
        int hour = calendar.get(Calendar.HOUR_OF_DAY); // 时
        int minute = calendar.get(Calendar.MINUTE); // 分
        int second = calendar.get(Calendar.SECOND); // 秒
        int day = calendar.get(Calendar.DAY_OF_WEEK); // 星期，1为星期日、2为星期1，以此类推

        Calendar date1 = Calendar.getInstance(); // 日期比较
        Calendar date2 = Calendar.getInstance();
        date1.set(2017, 1, 1);
        date2.set(2018, 1, 1);
        if (date1.before(date2)) { System.out.println('date1在date2之前'); }
    }
}

匿名类

interface IDatabase { void connect (String connString); }

public class Main {
    public static void main (String[] args) {
        // 线上类
        class Oracle implements IDatabase {
            @Override
            public void connect (String connString) { System.out.println('连接Oracle'); }
        }
        IDatabase oracle = new Oracle();
        oracle.connect('ip/uid/pwd');

        // 匿名类
        IDatabase mysql = new IDatabase() {
            @Override
            public void connect (String connString) { System.out.println('连接MySQL'); }
        };
        mysql.connect('ip/uid/pwd');
    }
}

lambda

import java.util.function.BiFunction; // 方法型接口(java.util.function)
import java.util.function.Function;
import java.util.HashMap; // HashMap
import java.util.Map;

interface IDatabase { void update (); } // 单方法无参数接口

public class Main {
    public static void main (String[] args) {
        // Lambda 与单方法无参数接口
        IDatabase blogDB = () -> { System.out.println('更新博客数据库'); };
        blogDB.update();

        // Lambda 与方法型接口 Function<T:参数类型,R:返回值类型>
        Function<Integer, Integer> multi2 = (i) -> { return i * 2; };
        System.out.println(multi2.apply(10));

        // Lambda 与方法型接口 BiFunction<T:第1参数类型,U:第2参数类型,R:返回值类型>
        BiFunction<Integer, Integer, Integer> addfunc = (a, b) -> { return a + b; };
        System.out.println(addfunc.apply(10, 20));

        // Lambda 与 HashMap 使用
        Map<String, String> stringMap = new HashMap<>();
        stringMap.put('usa', '美国');
        stringMap.put('chn', '中国');
        for (Map.Entry<String, String> item : stringMap.entrySet()) { System.out.println('.' + item.getKey() + ':' + item.getValue()); }
        stringMap.forEach((key, value) -> { System.out.println('.' + key + ':' + value); });
    }
}

stringBuffer stringBuilder

public class Main {
    public static void main (String[] args) {
        StringBuffer stringBuffer = new StringBuffer(); // StringBuffer 线程安全
        stringBuffer.append('我学习Java');
        stringBuffer.append('我学习Android');
        System.out.println(stringBuffer.toString());

        StringBuilder stringBuilder = new StringBuilder(); // StringBuilder 速度优势
        stringBuilder.append('我学习Java');
        stringBuilder.append('我学习Android');
        System.out.println(stringBuilder.toString());
    }
}

定时

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

public class Main {
    public static void main (String[] args) {
        SimpleDateFormat format = new SimpleDateFormat('[HH:mm:ss]'); // 日期格式化输出

        class MyTimerTask extends TimerTask {
            @Override
            public void run () { System.out.println(format.format(new Date()) + 'MyTimerTask.run()...'); }
        }

        Timer timer = new Timer();
        timer.schedule(new MyTimerTask(), 1000, 3000);
    }
}