public static void main(String[] args){ 
Integer a1 = 100; 
Integer b1 = a1;//另一种也可以b1=100 
Field field = null; 
try { 
field = a1.getClass().getDeclaredField("value"); 
} catch (NoSuchFieldException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} catch (SecurityException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} 

field.setAccessible(true); 

try { 
field.set(a1, 5000); 
} catch (IllegalArgumentException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} catch (IllegalAccessException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} 
System.out.println("b1="+b1); 

Integer c1 = 100; 
System.out.println("c1="+c1); 

} 

public static void main(String[] args){ 
Integer a1 = 200; 
Integer b1 = a1; 
Field field = null; 
try { 
field = a1.getClass().getDeclaredField("value"); 
} catch (NoSuchFieldException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} catch (SecurityException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} 

field.setAccessible(true); 

try { 
field.set(a1, 5000); 
} catch (IllegalArgumentException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} catch (IllegalAccessException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} 
System.out.println("b1="+b1); 

Integer c1 = 200; 
System.out.println("c1="+c1); 

} 

public static void main(String[] args){ 
Integer a1 = new Integer(100); 
Integer b1 = a1; 
Field field = null; 
try { 
field = a1.getClass().getDeclaredField("value"); 
} catch (NoSuchFieldException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} catch (SecurityException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} 

field.setAccessible(true); 

try { 
field.set(a1, 5000); 
} catch (IllegalArgumentException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} catch (IllegalAccessException e) { 
// TODO Auto-generated catch block 
e.printStackTrace(); 
} 
System.out.println("b1="+b1); 

Integer c1 = 100; 
System.out.println("c1="+c1); 

}

   基本类型和包装类的对应 
  byte  Byte 
  short  Short 
  int  Integer 
  long  Long 
  float  Float 
  double  Double 
  char  Character 
  boolean  Boolean 

public class Demo_Integer { 
 public static void main(String[] args) { 
//JDK1.5之前 
 int a = 100; 
 Integer a1 = new Integer(a); //将基本数据类型包装成对象,装箱 
 int b = a1.intValue(); //将对象转换为基本数据类型,拆箱 
//JDK1.5之后 
 int x = 100; 
 Integer x1 = x;  //自动装箱,把基本数据类型转换为对象 
 int y = x1 + x;  //自动拆箱,把对象转换为基本数据类型 
 } 
} 

public class Demo_Integer { 
 public static void main(String[] args) { 
  Integer a = null; 
  int b = a + 100; //自动拆箱底层将会调用a.intValue(),a为null,自然会抛出 NullPointerException 
  System.out.println(b); 
 } 
} 

public class Demo_Integer { 
 public static void main(String[] args) { 
  Integer i1 = new Integer(97); 
  Integer i2 = new Integer(97); 
  System.out.println(i1 == i2); 
  System.out.println(i1.equals(i2)); 
  System.out.println("-----------"); 
  
  Integer i3 = new Integer(197); 
  Integer i4 = new Integer(197); 
  System.out.println(i3 == i4); 
  System.out.println(i3.equals(i4)); 
  System.out.println("-----------"); 
 } 
} 

Output: 
 false 
 true 
 ----------- 
 false 
 true 
 ----------- 

public class Demo_Integer { 
 public static void main(String[] args) { 
  Integer i1 = 127; 
  Integer i2 = 127; 
  System.out.println(i1 == i2); 
  System.out.println(i1.equals(i2)); 
  System.out.println("-----------"); 
 
  Integer i3 = 128; 
  Integer i4 = 128; 
  System.out.println(i3 == i4); 
  System.out.println(i3.equals(i4)); 
  System.out.println("-----------"); 
 } 
} 

Output: 
true 
true 
----------- 
false 
true 
----------- 

public final class Integer extends Number implements Comparable<Integer> { 
 public static Integer valueOf(int i) { 
  //当 i >= -128 且 i <= 127 时,会直接将取缓冲区中的对象 
  if (i >= IntegerCache.low && i <= IntegerCache.high) 
   return IntegerCache.cache[i + (-IntegerCache.low)]; 
  return new Integer(i);//超过了byte取值范围会在堆内存创建 
 } 
 
 //内部类充当缓冲区 
 private static class IntegerCache { 
  static final int low = -128; 
  static final int high; 
  static final Integer cache[]; 
 
  static { 
   // high value may be configured by property 
   int h = 127; 
   String integerCacheHighPropValue = 
    sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high"); 
   if (integerCacheHighPropValue != null) { 
    try { 
     int i = parseInt(integerCacheHighPropValue); 
     i = Math.max(i, 127); 
     // Maximum array size is Integer.MAX_VALUE 
     h = Math.min(i, Integer.MAX_VALUE - (-low) -1); 
    } catch( NumberFormatException nfe) { 
     // If the property cannot be parsed into an int, ignore it. 
    } 
   } 
   high = h; 
 
   cache = new Integer[(high - low) + 1]; 
   int j = low; 
   for(int k = 0; k < cache.length; k++) 
    cache[k] = new Integer(j++); 
 
   // range [-128, 127] must be interned (JLS7 5.1.7) 
   assert IntegerCache.high >= 127; 
  } 
   private IntegerCache() {} 
 } 
  
}