Java-类型转换，String转Object和Object转String

import java.text.MessageFormat;
import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * 
 * @author  课时二 ：类型转换
 *
 */
public class TypeConvert {

	public static void main(String[] args) {
		/**
		 * 1. 隐式转换：小类型转大类型自动转换 2.强制转换：大类型转小类型强制转换
		 */
		Byte bt = 1;
		int num = 100;
		// 隐式转换
		short stNumBt = bt;
		// int to short强制转换
		short stNum = (short) num;

		// String转换成Object
		StringToObject();
		
		System.out.println();
		System.out.println("********************************************************分界线******************************************************************");
		System.out.println();
		
		//Object转换成String
		ObjectToString();

	}

	/**
	 * String转换成Object
	 */
	public static void StringToObject() {

		String intStr = "10000";
		String boolStr = "true";
		String doubleStr = "20.88";
		String dateStr = "2019-1-1 10:10:10";

		// String to int 方法一
		int IntNum = Integer.parseInt(intStr);
		System.out.printf("String to int:%d", IntNum);
		System.out.println();

		// String to int 方法二
		int IntNum2 = Integer.valueOf(intStr);
		System.out.printf("String to int: %d ", IntNum2);
		System.out.println();

		// String to boolean 方法一
		boolean bl = Boolean.parseBoolean(boolStr);
		System.out.printf("String to boolean: %b ", bl);
		System.out.println();

		// String to boolean 方法二
		boolean bl2 = Boolean.valueOf(boolStr);
		System.out.printf("String to boolean: %b ", bl2);
		System.out.println();

		// String to Date
		SimpleDateFormat simpleDate = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		Date dt = simpleDate.parse(dateStr, new ParsePosition(0));
		System.out.printf("String to Date: %tF %tT", dt, dt);
		System.out.println();
		System.out.println(dt);

		// String to double
		double db = Double.valueOf(doubleStr);
		System.out.printf(" String to double: %.2f", db);
		System.out.println();

	}

	/**
	 * Object转换成String
	 */
	public static void ObjectToString() {
		int num = 1;
		boolean isExists = true;
		double db = 20.88;
		Date dt = new Date();

		// Int to String方法一
		String numString = Integer.toString(num);
		System.out.printf("Int to String:%s", numString);
		System.out.println();

		// Int to String方法二
		String numString2 = String.valueOf(num);
		System.out.printf("Int to String2:%s", numString2);
		System.out.println();

		// boolean to String方法一
		String boolString = Boolean.toString(isExists);
		System.out.printf("boolean to String:%s", boolString);
		System.out.println();

		// boolean to String方法二
		String boolString2 = String.valueOf(isExists);
		System.out.printf("boolean to String2:%s", boolString2);
		System.out.println();

		// double to String方法一
		String doubleString =Double.toString(db);
		System.out.printf("double to String:%s", doubleString);
		System.out.println();

		// double to String方法二
		String doubleString2 = String.valueOf(db);
		System.out.printf("double to String2:%s", doubleString2);
		System.out.println();

		// Date to String 方法一
		String dtString = String.valueOf(dt);
		System.out.printf("Date to String:%s", dtString);
		System.out.println();
		
		SimpleDateFormat sdDateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		String dtString2=sdDateFormat.format(dt);
		System.out.printf(MessageFormat.format("Date to String:{0}", dtString2));
		System.out.println();
		
		

	}

}

总结：

String 转换 Object : 使用类似 Obj.parseObj(String) , Obj.valueOf(String)

Object转换 String: 使用类似 Obj.toString(Obj), String.valueOf(Obj)

Date类型的转换使用SimpleDateFormat

如果是 JDK8 的应用，可以使用 Instant 代替 Date，LocalDateTime 代替 Calendar， DateTimeFormatter 代替 SimpleDateFormat，

执行效果：