【JAVA】java基础语法_java基础语法菜鸟教程
Java基础语法总结
1. 变量
- 定义:变量是存储数据的容器。
- 语法:数据类型 变量名 = 值;
- 示例:
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int age = 25;
String name = "Alice";
2. 数据类型
- 基本数据类型:byte, short, int, long, float, double, char, boolean
- 引用数据类型:类、接口、数组等
- 示例:
- java复制代码
- byte b = 100;
- int i = 2147483647;
- float f = 3.14f;
- double d = 3.141592653589793;
- char c = 'A';
- boolean truth = true;
3. 运算符
- 算术运算符:+, -, *, /, %
- 比较运算符:==, !=, >, <, >=, <=
- 逻辑运算符:&&, ||, !
- 位运算符:&, |, ^, ~, <<, >>, >>>
- 赋值运算符:=, +=, -=, *=, /=
- 示例:
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byte b = 100;
int i = 2147483647;
float f = 3.14f;
double d = 3.141592653589793;
char c = 'A';
boolean truth = true;
4. 控制结构
- 条件语句:if, else if, else
- 循环语句:for, while, do-while
- 示例:
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int num = 10;
// 条件语句
if (num > 0) {
System.out.println("Number is positive.");
} else if (num < 0) {
System.out.println("Number is negative.");
} else {
System.out.println("Number is zero.");
}
// 循环语句
for (int i = 0; i < 5; i++) {
System.out.println("Iteration: " + i);
}
int count = 0;
while (count < 5) {
System.out.println("While loop: " + count);
count++;
}
count = 0;
do {
System.out.println("Do-while loop: " + count);
count++;
} while (count < 5);
5. 函数
- 定义:函数是一段可以重复使用的代码,用于执行特定任务。
- 语法:返回类型 函数名(参数列表) { 函数体 }
- 示例:
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// 无参数无返回值
void printHello() {
System.out.println("Hello, World!");
}
// 有参数有返回值
int add(int a, int b) {
return a + b;
}
// 调用函数
public class Main {
public static void main(String[] args) {
printHello();
int result = add(5, 3);
System.out.println("Result: " + result);
}
}
应用场景和示例代码
场景一:计算两个数的和并判断其奇偶性
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import java.util.Scanner;
public class SumAndParity {
// 函数:计算两个数的和
public static int sum(int a, int b) {
return a + b;
}
// 函数:判断一个数是否为偶数
public static boolean isEven(int number) {
return number % 2 == 0;
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter first number:");
int num1 = scanner.nextInt();
System.out.println("Enter second number:");
int num2 = scanner.nextInt();
int result = sum(num1, num2);
System.out.println("Sum: " + result);
if (isEven(result)) {
System.out.println("The sum is even.");
} else {
System.out.println("The sum is odd.");
}
scanner.close();
}
}
场景二:计算斐波那契数列的前N项
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public class Fibonacci {
// 函数:计算斐波那契数列的第n项
public static int fibonacci(int n) {
if (n <= 1) {
return n;
}
return fibonacci(n - 1) + fibonacci(n - 2);
}
public static void main(String[] args) {
int n = 10; // 假设我们要计算前10项
System.out.println("Fibonacci series up to " + n + " terms:");
for (int i = 0; i < n; i++) {
System.out.print(fibonacci(i) + " ");
}
}
}
场景三:判断一个数是否为质数
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public class PrimeChecker {
// 函数:判断一个数是否为质数
public static boolean isPrime(int number) {
if (number <= 1) {
return false;
}
for (int i = 2; i <= Math.sqrt(number); i++) {
if (number % i == 0) {
return false;
}
}
return true;
}
public static void main(String[] args) {
int number = 29; // 假设我们要判断29是否为质数
if (isPrime(number)) {
System.out.println(number + " is a prime number.");
} else {
System.out.println(number + " is not a prime number.");
}
}
}