Arrays and class packaging

public static void main(String[] args) {

        int[] arr = {33,22,11,44,66,55};
        System.out.println(Arrays.toString(arr));    //输出  [33, 22, 11, 44, 66, 55]
        Arrays.sort(arr);            //   排序了
        System.out.println(Arrays.toString(arr)); 
        int[] arr2 = arr;
        //System.out.println(Arrays.toString(arr2));
        System.out.println(Arrays.binarySearch(arr2, 22));    //   二分查找法   binarySearch()
        System.out.println(Arrays.binarySearch(arr2, 66));
        
    }

 

Basic data types packaging

　　int    -- >    Integer

　　char   -- >   Charater

　　Six other initial capital letters

 

Interger:

　　Construction method     

　　　　Interger(int value )

　　　　Number strings int Interger (String str) can for example "123"

　　Two constants

　　　　 Maximum number of MAX_VALUE MIN_VALUE minimum number that can be represented int

　　

static void main public (String [] args) { 
        System.out.println (Integer.toBinaryString (60)); // switch to a binary 111100 
        // octal 74; System.out.println (Integer.toOctalString (60)) 
        the System .out.println (Integer.toHexString (60)); // hexadecimal. 3C 
    }

 

int -> String
　　string concatenation, String of valueOf (int)

　　toString Integer object ()　　

　　 Integer.toString (int i) static method

 

String -> int
　　. 1, to turn into Interger (string constructor pass) then intValue ()   

　　2、Interger.parseInt(String str)

public static void main(String[] args) {
        String  b1 = "true";
        boolean b = Boolean.parseBoolean(b1);
        System.out.println(b);
        
        String s1 = "abs";
        char [] arr = s1.toCharArray();
        
        //demo();
    }

    public static void demo() {
        String s1 = "200";
        Integer i1 = new Integer(s1);
        int i2 = i1.intValue();
        System.out.println(i2);
        
        int i3 = Integer.parseInt(s1);    // 推荐用这个
        System.out.println(i3);
    }

 

 

Basic data types of packaging has eight, seven of which have parseXxx ():
　　to convert the string representation to the data type


　　automatic boxing and unboxing automatically (hereinafter Jdk1.5 only)

　　　　　　Autoboxing: Interger i = 200; 200 automatically packaged as objects Interger

　　　

Wave i1 = 97;

        97 I2 = Integer; 
        syso (== I1 I2) to true 
        
        Integet 128 = I3; 
        Integer I4 = 128; 
        syso (== I3 I4) to false 
        
        Cause: -128 to 127 autoboxing byte is the range, in this range within autoboxing does not create a new object, taken directly from the constant pool, the address is the same value