Java operators

PS: At the lowest level, data in Java is manipulated by using operators.

Use of operators and their precedence

The following is the complete code (1):

package cxcf;
public class Day3 {
    public static boolean fun1(int val){
        System.out.println("val<1");
        return val<1;//true
    }
    public static boolean fun2(int val){
        System.out.println("val<2");
        return val<2;//false
    }
    public static boolean fun3(int val){
        System.out.println("val<3");
        return val<3;
    }

    //void 方法的返回值
    //Max2 方法名称
    //(int a,int b) 形式参数  形参
    public static int Max2(int a,int b){
        if(a>b){
            return a;
            //System.out.println(a);
        }else{
            return b;
            //System.out.println(b);//()函数
        }       
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        boolean b5=fun1(0)&&fun2(2)&&fun3(1);//短路 与，有一个为false,短路
        System.out.println(b5);
        boolean b6=fun1(0)||fun2(2)||fun3(1);//有一个为true,短路
        System.out.println(b6);

        // ! && || 只支持boolean值
        boolean b1=true;
        boolean b2=false;
        if(!b1==true){
            System.out.println("is true");
        }else{
            System.out.println("is false");
        }

        int[] array={1,2,3,4,5};//[] 声明是一个数组
        array[0]=2;//[]属性获取 下标里面的内容
        System.out.println(array);
        System.out.println(array[0]);
        int len=array.length;//方法调用 

        System.out.println(len);
        int a=10;
        int b=20;
        //Max2(a,b);
        int e=Max2(a,b);
        System.out.println(e);
        int c=30;//= 赋值号
        int d=40;//代码冗余 
    }
}


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• Break down the code:
• 1. Notes on [ ], . , ( ):
  (1) array[ ] declares an array;
  (2) array[0]=2; the attribute gets the content in the subscript;
  (3) "." array.length; Call method;
  (4) ( ) can be used to create a function:
  public void int Max2(int a,int b)
• 2. Logical operators "AND" && "OR" || "NOT"! , can generate a Boolean value according to the logical relationship of the parameters, and only the Boolean value can be applied, :
  (1) Short circuit
  When using logical operators, a phenomenon will be encountered, that is, once the value of an expression can be determined, The rest of the expression is no longer evaluated.
  boolean b5=fun1(0)&&fun2(2)&&fun3(1);//Short-circuit and, if one of them is false, short-circuit and no longer output;
  boolean b6=fun1(0)||fun2(2)|| fun3(1);//Short-circuit or, if one of them is true,
  the output will not be calculated later; the
  output result:
  

---

The following is the complete code (2):

package cxcf;
public class Day31 {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        // ++ 后置++ 前置++
        int a1=10;
        a1++;
        ++a1;//单个写没有任何区别
        int a2=a1++;//tmp=a2; a3=tmp; a2+1;
        int a4=++a2;//a2+1 a4
        System.out.println(a2);
        System.out.println(a4);

        //算余数
        System.out.println(10%3);
        System.out.println(-10%3);
        System.out.println(-10%-3);//取商取在绝对值以内
        System.out.println(10%-3);
        System.out.println("========");

        float f1=5/2;
        float f2=(float)5.0/2;
        float f3=(float)5/2;
        float f4=5/(float)2;
        System.out.println(f1);//5是int类型，取整   2.0
        System.out.println(f2);//2.5
        System.out.println(f3);//2.5
        System.out.println(f4);//2.5

        short sh=1;
        short sh2=(short)(sh+1);
        sh+=1;//sh=sh+1;-=  *=  /=
        //instanceof 比较类型
    }
}

• Break down the code:
• Arithmetic operators: addition,
  subtraction, multiplication and division "+ - * / ";
  remainder "%";
  (10%3), (-10%3), (-10%-3), (10%-3) The output of the situation is "1, -1, -1, 1";
  assignment number, assign the value after the symbol to the preceding "=";
  "+=, -=, *=, /=, %=", a+= b; equivalent to a=a+b, the rest are the same;

• Auto-increment and decrement "++-":
  a1++; and ++a1; do not make any difference in single writing;
  int a2=a1++; assign first and then add and subtract;
  int a4=++a2; add and subtract first and then assign.

• Bitwise operator
  "&": bitwise AND: 0 in case of 0;
  "|" bitwise OR: 1 in case of 1;
  "~" bitwise negation: unary operator;
  "^" bitwise XOR: both are 0 , the difference is 1;
  Tips: The bitwise operator can be used in combination with (=), "&=, |=, ^=", this is legal, since "~" is a unary operator, it cannot be used with (= ) combined.

• Shift operator:
  "<<" left shift (low-order zeros):
  ">>" right-shift (if the high-order symbol is 0, insert 0 in the high-order, if it is 1, insert 1 in the high-order);
  ">>>" none Sign right shift operator (no matter whether it is positive or negative, the high bit is inserted with 0);
  

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Supplement: error-prone points:
float f1=5/2; the output is 2, both of which are int types;
float f2=(float)5.0/2; the output is 2.5;
float f3=(float)5/2; the output is 2.5;
float f4=5/(float)2; output is 2.5;

short sh=1;
short sh2=(short)(sh+1);1 is of type int and must be converted, otherwise an error will be reported.