A new feature of Java13-5 JDK1.5 and an integer face question

1. New features of JDK5
Auto-boxing: converting a base type to a wrapper class type
Auto-unpacking: converting wrapper class types to basic types

Note a small problem:
When used, Integer x = null; The code appears Nullpointerexception.
Standardization: It is recommended that you first determine whether it is null before you use it.

1  public classIntegerdemo {2  public Static voidmain (string[] Args) {3 //defines a wrapper class type variable i for an int type4 //integer i = new integer (+);5Integer II = 100;6II + = 200;7System.out.println ("ii:" +ii);8 9 //through the post-compilation codeTen //Integer II = integer.valueof (+);//Automatic Boxing one //II = integer.valueof (ii.intvalue () + +);//automatic unpacking and automatic packing a //System.out.println ((new StringBuilder ("ii:")). append (ii). toString ()); -  -Integer III =NULL; the //NullPointerException - if(iii! =NULL) { -III + = 1000; - System.out.println (iii); +}//This is a dead code, never coming in. - } +}

2. Interview Questions:

First Question:
Integer i = 1;
i + = 1;
What does this piece of code do?

Answer: Integer i = 1; Auto Boxing
i + = 1; Automatic unpacking and Automatic packing

The second question:
See how the program writes results
　

1  public classIntegerdemo {2  public Static voidmain (string[] Args) {3Integer I1 =NewInteger (127);4Integer i2 =NewInteger (127);5System.out.println (i1 = =i2);6 System.out.println (i1.equals (i2));7System.out.println ("-----------");8 9Integer i3 =NewInteger (128);TenInteger I4 =NewInteger (128); oneSystem.out.println (i3 = =i4); a System.out.println (i3.equals (i4)); -System.out.println ("-----------"); -  theInteger i5 = 128; -Integer I6 = 128; -System.out.println (i5 = =i6); - System.out.println (i5.equals (i6)); +System.out.println ("-----------"); -  +Integer i7 = 127; aInteger i8 = 127; atSystem.out.println (i7 = =i8); -System.out.println (i7.equals (i8));

The answer Above: the Equals method is true, and the answer to = = Is: Flase,flase,flase,true
By looking at the source code, we know that a data buffer pool is made for data between 128 and 127.
If the data is within that range, extract the data directly from the buffer pool without creating a new space
If the data is not in this range, you will need to recreate the new space
So System.out.println (i5 = = i6); this is Flase.
Integer II = integer.valueof (127);
}
}

Note: integer data is directly assigned, if between 128 and 127, the data is fetched directly from the buffer Pool.

A new feature of Java13-5 JDK1.5 and an integer face question