Date之Parse和clone

public static void main(String[] args) throws CloneNotSupportedException, ParseException {	
		SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
		// test parse date
		Date date = new Date();
		Date date1 = date;
		System.out.println(date == date1);   // 两个引用指向同一个对象
		System.out.println(sdf.format(date1));
		date1 = sdf.parse("20170625");  // parse会重新创建了一个date对象
		System.out.println(date == date1);  // false,不同的引用
		System.out.println(sdf.format(date1)); // 打印验证
		System.out.println(sdf.format(date));
		
		// test clone date
		Date date2 = new Date();
		Date date3 = (Date) date2.clone();
		System.out.println(date2 == date3); // false,说明创建了新对象
		
		// test string
		String str1 = "123";
		String str2 = str1;
		System.out.println(str2 == str1);
		System.out.println(str2);
		str2 = "456";  // 创建了新对象
		System.out.println(str2 == str1); // false
		System.out.println(str2);
		System.out.println(str1);
	}