Java-类型转换，String转Object和Object转String

骑猪看日落 2021-12-11 03:01 658阅读 0赞

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：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdWNoYW5nMTk5NTA3MDM_size_16_color_FFFFFF_t_70][]

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