Java包装类之自动装箱与拆箱

public class WrapperTest {

     // 基本数据类型--->包装类：调用包装类的构造器

     @Test

     public void test1() {

         int num1 = 10 ;

         Integer in1 = new Integer(num1);

         System.out.println(in1.toString()); //10

         Integer in2 = new Integer( "123" );

         System.out.println(in2.toString()); //123

         // 报异常:NumberFormatException

         Integer in3 = new Integer( "123abc" ); //调用Integer必须全是数字

         System.out.println(in3.toString());

         //有点特殊：因为底层源码 return ((s != null) && s.equalsIgnoreCase("true"));

         Boolean b1 = new Boolean( true );

         Boolean b2 = new Boolean( "True" ); //true

         System.out.println(b2);

         Boolean b3 = new Boolean( "true123" ); //flase

         Order order = new Order();

         System.out.println(order.isMale); //false//因为基本数据类型的默认初始化值为：false

         System.out.println(order.isFamale); //null//此时为引用数据类型(类),默认初始化值：null

     }

}

class Order {

     boolean isMale;

     Boolean isFamale;

}

public class WrapperTest {

     @Test

     public void test2() {

         Integer in1 = new Integer( 12 );

         int i1 = in1.intValue();

         System.out.println(i1 + 1 ); //13

         Float f1 = new Float( 12.3 );

         float f2 = f1.floatValue();

         System.out.println(f2 + 1 ); //13.3

     }

}

public class WrapperTest {

     @Test

     public void test3() {

         //自动装箱

         int num2 = 10 ;

         Integer in1 = num2;

         boolean b1 = true ;

         Boolean b2 = b1;

         //自动拆箱

         System.out.println(in1.toString());

         int num3 = in1;

     }

}

public class WrapperTest {

     @Test

     public void test4() {

         //方式一：连接运算

         int num1 = 10 ;

         String str1 = num1 + "" ;

         //方式二：调用String的valueOf(Xxx xxx)

         float f1 = 12 .3f;

         String str2 = String.valueOf(f1);

         Double d1 = new Double( 12.4 );

         String str3 = String.valueOf(d1);

         System.out.println(str2); //"12.3"

         System.out.println(str3); //"12.4"  

     }

}

public class WrapperTest {

     @Test

     public void test5() {

         String str1 = "123" ;

         int num2 = Integer.parseInt(str1); //若为"123a",则会报NumberFormatException

         System.out.println(num2 + 1 );

         String str2 = "true" ;

         boolean b1 = Boolean.parseBoolean(str2); //非true,即flase

         System.out.println(b1);

     }