We can use java program operation, we need to master data types, constants, variables and operators
About the data type I have summarized a Excel spreadsheet, the range in which the single-precision floating-point and double-precision floating-point calculation is not accurate.
Constants are running during the java fixed data, can be printed
public class Demo {
public static void main (String [] args) {
final int C =. 1; // create a constant, integer type, constant final keyword to define
System.out.println (C); // output: 1
}
}
Refers to the variable data can change during the java program is running, it can be printed
public class Variable {
public static void main (String [] args) {
int NUM = 50; // create a variable format: Data type variable name = data value
System.out.println (NUM); // Output: 50
int Number; // create a variable format: data type variable name;
Number = 3; // stored data into a variable: variable name = data value
System.out.println (Number); // output: 3.
Double d; // create a double-precision floating-point type of a variable, the variable name is named d
= 3.3 D; // stored data to a variable, the data value 3.3
System.out.println (D); // print output variable d, the output: 3.3
a float KK;
KK = 3.2F; // float which The default type is double, if we must use the float type, the need to add a suffix F.
System.out.println (KK); // output: 3.2
}
}
How to verify constant during the run java program fixed, variable can change?
public class the Test {
public static void main (String [] args) {
final int A =. 1; // create a constant, constants used to define the final keyword
System.out.println (A); // Output:. 1
final int 10 = b; // create a constant
// SB = "20"; // modify the values of the constants, will complain, can not run.
// workaround, delete or modify comments, because in doing exercises, so select the Notes to facilitate understanding during this review.
System.out.println (B); // Output: 10
int C = 100; //Create a variable assignment 100
C = 200; // modify a variable
System.out.println (C); // Output: 200
}
}
Operators are symbols constant and variable operating a equal sign operator is used in practice, the assignment operator.
Arithmetic:
public class Demo1 {
public static void main(String[] args) {
int a = 66;
int b = 66;
int r1 = a * b;
System.out.println(r1); //输出：4356，想要验算，可以使用手机or电脑上的计算器再计算一遍。
int r2 = a + b; //加法运算符
System.out.println(r2); //输出：132
int r3 = a - b; //减法运算符
System.out.println(r3); //输出：0
int r4 = a / b; //除法运算符
System.out.println(r4); //输出：1
int x =10;
int y =3;
int result = x%y; //模运算符
System.out.println(result); //10除以3，等于3余数1
}
}
逻辑运算符：
什么是逻辑？
简单打个比方，我们去超市购物，想要买一把雨伞
在收银台结算时，通常问默会自己，买没买雨伞。
这里的回答就是一种逻辑上的运算，买or没买。
是与否、有与无也都是逻辑的判断
public class Demo2{
public static void main(String[] args) {
boolean a = true;
boolean b = false;
System.out.println(a&&b); //输出：false。&&逻辑与运算符，仅当两个操作都为真，条件才为真。
System.out.println(a||b); //输出：true。逻辑或运算符，两个操作其中有一个为真，条件为真。
System.out.println(!a); //输出：false。逻辑非运算符，取反。
/* 这就是多行注释
* 与“&&”，或“||”，具有短路效果：
* 如果根据左边已经可以判断得到最终结果，那么右边的代码不再执行，从而节省一定的性能。
*
* 类比：斗地主时，我的牌是4和10，对方只有一张牌，我要如何出？
* 先出10，如果对方剩下的牌是5-10，那么我这局就赢了。
* 这在就是斗地主中，短路效果的应用。
*/
}
}
自增自减运算符
public class Demo3 {
public static void main(String[] args) {
int x = 1;
x++; //变量x自增1
System.out.println(x); //输出：2。因为变量x自增了1
int y = 1;
y--; //变量y自减1
System.out.println(y); //输出：0。因为变量y自减了1。
//自增自减符号，单独使用时，符号在前在后都一样。
//与其它混合使用时，如果，运算符在前，那么结果就要先增减，后打印。反之，符号在后，就先打印。
int a = 1; //运算符在前，那么结果就要先增减，后打印
System.out.println(++a); //输出：2。
int b = 1;
System.out.println(b--); //符号在后，就先打印，后自减。所以输出是1，输出后b的值自减1。
//如何看到b的值是否自减了呢？ 将变量b打印输出即可
System.out.println(b); //自减之后变量b的值是0，所以输出：0
}
}