Day4 operator, self increasing, self decreasing, logical operator, bit operation, binary conversion decimal, ternary operator, package mechanism, document comment

Operator

Self increasing , Self reduction

package operator;

public class Demo04 {
    
    public static void main(String[] args) {
    
        //++ --  Self increasing , Self reduction   Unary operator 
        int a= 3;

        int b = a++;  // After executing this line of code , First give b assignment , Since the increase again 
        // a = a+1
        System.out.println(a);

        // a = a+1;
        int c = ++a; // Before this line of code is executed , First of all, increase by yourself , Give again b assignment 

        System.out.println(a);
        System.out.println(b);
        System.out.println(c);

        // Power operation  2*3 2*2*2 = 8  Many operations are operated by tool classes ！
        double pow = Math.pow(2,3);
        System.out.println(pow);
    }
}
 Output 
4
5
3
5
8.0

Logical operators

package operator;

// Logical operators 
public class Demo05 {
    
    public static void main(String[] args) {
    
        //  And (and)  or （or）  Not （ Take the opposite ）
        boolean a = true;
        boolean b = false;

        System.out.println("a && b:"+(a && b)); // Logic and computation ： Both variables are true , The result is true
        System.out.println("a || b:"+(a||b)); // Logic or operation ： One of the two variables is true , The result is true
        System.out.println("! (a && b):"+!(a&&b)); // If it is true , It becomes false , If it is false, it becomes true 

        // Short-circuit operation 
        int c = 5;
        boolean d = (c<4)&&(c++<4);
        System.out.println(d);
        System.out.println(c);
         Output 
        a && b:false
		a || b:true
		! (a && b):true
		false
		5

An operation

package operator;

// An operation 
public class Demo06 {
    
    public static void main(String[] args) {
    
        /* A = 0011 1100 B = 0000 1101 A&B = 0000 1100(“ And ” all 1 by 1) A|B = 0011 1101（“ or ” There is one 1 Then for 1） A^C =0011 0001（“ Exclusive or ” Same as 0, Different for 1） ~B = 1111 0010（“ Take the opposite ” The opposite ） 2*8 = 16 2*2*2*2  Very efficient  << Move left  *2 >> Move right  /2, When the arrow points that way, it's called moving  0000 0000 0 0000 0001 1 0000 0010 2 0000 0011 3 0000 0100 4 0000 1000 8 0001 0000 16 */

        System.out.println(2<<3);
    }
}
 Output 
16

Binary to decimal

    0000 0000  0           Binary default 0
    0000 0001  1           From left to right 0~7, be 2^0 = 1
    0000 0010  2	       2^1 = 2  
    0000 0011  3	       2^1 + 2^0 = 3 
    0000 0100  4	       2^2 = 4 
    0000 1000  8	       2^3 = 8 
    0001 0000  16	       2^4 =16

String connector +

package operator;

public class Demo07 {
    
    public static void main(String[] args) {
    
        int a = 10;
        int b = 20;

        a += b; //a = a + b
        a -= b; //a = a - b

        // String connector  + , String
        System.out.println(a + b);
        System.out.println("" + a + b); // String before , The back will be spliced 
        System.out.println(a + b + ""); // String after , The front can calculate 
    }
}
 Output 
30
1020
30

Ternary operator

package operator;

// Ternary operator 
public class Demo08 {
    
    public static void main(String[] args) {
    
        // x ? y : z
        // If x == true, The result is y, Otherwise z

        int score = 80;
        String type = score < 60 ?" fail, ":" pass ";
        // if
        System.out.println(type);
    }
}
 Output 
 pass 

Packet mechanism

Pay attention to Idea Created in com.baidu When a child package cannot be created automatically

Click the pinion at the top right of the project structure on the left ,
Uncheck the compact middle packlages Options , At this point you build a com.itheima.package package ,
It will be shown as com It's a bag itheima package ,itheima It's a bag package.java!

import com.jiao.*; // Import all classes under this package

Documentation Comments

package com.jiao.base;

/** * @author John * @version 1.0 * @since 1.8 */
public class Doc {
    
    String name;

    /** * @param name * @return * @throws Exception */
    public String test(String name)throws Exception {
    

        return name;

    }
}

doc Order sample

javadoc -encoding UTF-8 -charset UTF-8 Doc.java