From the beginning to learn Java | entry and Java advanced (2) – operator, loop statement

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📚 operator.

📌 arithmetic operators (+, -, *, /, %)

📌 increment and decrement operators

The increment and decrement operators (+, -), ++, and – are unary operators and can be placed before or after operands. The operand must be an integer or floating-point variable that increases or decreases the value of the variable by one. The difference between ++x and x++ is that ++x executes x=x+1 before using the value of x, whereas x++ executes x=x+1 after using the value of x.

// 
int i = 10;
i++;
System.out.println(i); / / 11

int k = 10;
++k;
System.out.println(k); / / 11++ appears before a variable:int i = 10;
int k = ++i;
System.out.println(); / / 11
System.out.println(); / / 11++ appears after a variable:int i = 10;
int k = i++;
System.out.println(k); / / 10
System.out.println(i); / / 11

int i = 10;
System.out.println(i++); / / 10
// Unpack code:
int temp = i++;
System.out.println(temp); / / 10
System.out.println(i); / / 11

int i = 10;
System.out.println(++i); / / 11
// Unpack code:
int temp = ++i;
System.out.println(temp); / / 11
System.out.println(i); / / 11

// 原文出自: CSDN-请叫我阿ken
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📌 relational operators (>, >=, <, <=, ==,! =)

📌 logical operators (&, |,! , &&, | |)

A logical operator requires that both sides be Boolean and that the final result is still Boolean. & is true on both sides, the result is true | side is true, the result is true! In fact, the inverse && and & operation results are exactly the same, the difference lies in: && there is a short circuit phenomenon. When the left side is false: && short-circuited. On the left is true: | | short circuit.

📌 assignment operators (=, +=, -=, *=, /=, %=)

byte x = 100; // byte The maximum value is 127
x += 1000; // The compilation can pass, the x variable is still byte, but the precision is lost.

x += 1000; Equivalent to: x = (byte)(x + 1000);
int i = 10;
i += 10; // same as: I = I + 10; Accumulation.

// 原文出自: CSDN-请叫我阿ken
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📌 conditional operator

Ternary operator syntax: Boolean expressions? Expression 1: The Boolean expression of expression 2 is true, and expression 1 is selected as the result. Instead, choose expression 2 as the result.

📌 string concatenation operator

String name = "jackson"; System.out.println("Welcome to a successful landing."+name+"Come back");

// 原文出自: CSDN-请叫我阿ken
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📌 bit operator

Integer data is represented in binary form in memory. For example, a variable of type int takes up 4 bytes in memory and contains 32 bits. The binary representation of type int 7 is:

00000000 00000000 00000000 00000111
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The highest bit on the left is the sign bit. The highest bit is 0 for a positive number and 1 for a negative number. Negative numbers are represented by complement. For example, the complement of -8 is:

The complement, source, and inverse of positive numbers are the same. The complement of +8, the original, the inverse, is 0000, 1000. The complement, source and inverse of negative numbers are all placed in the sign bit with 1, and the following 7 bits are changed: the source of -8:1000, 1000; The inverse of -8:1111 0111; The complement of -8:1111 1000. // Please call me KenCopy the code

!!!!!!!!!!

📌 instanceof operator

📌switch Switch statement

switch(expression){caseConstant values1; Several statementsbreak;

caseConstant values2; Several statementsbreak; .caseConstant value n. Several statementsbreak;

default; Several statements}// The switvh expression can be byte, short, int, or char. Constants from 1 to n are also of byte, short, int, and char, and may differ from each other.

// 原文出自: CSDN-请叫我阿ken
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📚 loop statement

📌 while loop

• Its syntax mechanism and execution principle: while (Boolean expression) {

  The loop body. } If the Boolean expression is true, the loop body is executed. After the loop body is finished, the result of the Boolean expression is judged again. If it is still true, the loop body is executed again.

• Case loop:

while(true){
System.out.println("Dead loop");
}

// 原文出自: CSDN-请叫我阿ken
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Control statements

1. About loop statements for loop, while loop, do… While loop What is a loop statement and why do we use it? Because in the real world, there are many things that need to be done over and over again. To reduce the amount of code, use loop statements.

Requirements: First point: you must learn the grammatical structure by heart. Number two: you have to understand how they work. To implement cases, to implement features. Start with simple cases and work your way through the complex problems.

📌 do… The while loop

do{circulatory body; }while(Boolean expression);/* This last semicolon is crucial */

// 原文出自: CSDN-请叫我阿ken
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int i = 0;
do{
System.out.println(i); // 0 1 2 3... 8 and 9
i++;
// We can replace the previous two lines with
// System.out.println(i++);
}while(i < 10);

int i = 0;
do{
System.out.println(++i); // 1 2 3... 8 9 10
}while(i < 10);

int k = 100;
System.out.println(++k); / / 101
System.out.println(k);   / / 101

int m = 10;
System.out.println(m++); / / 10
System.out.println(m)    / / 11

// 原文出自: CSDN-请叫我阿ken
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📌for loop statement

for(expression1; expression2; expression3) {loop statement; }// 原文出自: CSDN-请叫我阿ken
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// anli
public class Example_n {
public static void main(String args[]){
long sum = 0, a = 8, item = a, n = 12, i = 1;
for(i = 1; i <= n; i++) {
sum = sum + item;
item = item*10+ a; } System.out.println(sum); }}// 原文出自: CSDN-请叫我阿ken
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If and switch are branch statements and select statements (select structures). For, while, do… While… These are loop statements (loop structures). Break, continue, and return belong to the turn structure. For and while are completely interchangeable except in different syntax.

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