10个简单的java代码教程演练

Java代码不会？这个问题可能很多人都遇到过，因为java语言本身就是一个开源的语言，所以很多人都觉得自己学不会，其实只要掌握了基本的知识，就可以轻松上手了。下面是几个简单的Java代码演练，涵盖了变量、条件语句、循环语句等核心概念，希望对大家有所帮助。如果你想学习java，可以参考一下这篇文章。

1. 变量和基本输出

```java

public class HelloWorld {

    public static void main(String[] args) {

        // 定义字符串和整数变量

        String name = "Alice";

        int age = 25;

        // 输出变量到控制台

        System.out.println("Hello, " + name + "!");

        System.out.println("You are " + age + " years old.");

    }

}

```

输出结果：

```

Hello, Alice!

You are 25 years old.

```

2. 条件语句

```java

public class Grade {

    public static void main(String[] args) {

        // 定义变量作为成绩

        int score = 85;

        // 根据成绩输出不同的等级

        if (score >= 90) {

            System.out.println("A");

        } else if (score >= 80) {

            System.out.println("B");

        } else if (score >= 70) {

            System.out.println("C");

        } else if (score >= 60) {

            System.out.println("D");

        } else {

            System.out.println("F");

        }

    }

}

```

输出结果：

```

B

```

3. 循环语句

```java

public class Count {

    public static void main(String[] args) {

        // 从1到10累加

        int sum = 0;

        for (int i = 1; i <= 10; i++) {

            sum += i;

        }

        // 输出累加结果

        System.out.println("1 + 2 + ... + 10 = " + sum);

    }

}

```

输出结果：

```

1 + 2 + ... + 10 = 55

```

4. 数组和循环

```java

public class ArraySum {

    public static void main(String[] args) {

        // 定义数组并初始化

        int[] arr = {1, 2, 3, 4, 5};

        // 遍历数组并求和

        int sum = 0;

        for (int i = 0; i < arr.length; i++) {

            sum += arr[i];

        }

        // 输出数组元素和

        System.out.println("The sum of array elements is " + sum);

    }

}

```

输出结果：

```

The sum of array elements is 15

```

5. 方法调用

```java

public class Calculator {

    public static void main(String[] args) {

        // 调用add方法

        int num1 = 10;

        int num2 = 5;

        int sum = add(num1, num2);

        // 输出结果

        System.out.println(num1 + " + " + num2 + " = " + sum);

    }

    // 定义add方法

    public static int add(int a, int b) {

        return a + b;

    }

}

```

输出结果：

```

10 + 5 = 15

```

6. 类和对象

```java

public class Rectangle {

    // 定义长和宽变量

    int length;

    int width;

    // 定义计算面积方法

    public int getArea() {

        return length * width;

    }

    public static void main(String[] args) {

        // 创建Rectangle对象并设置长和宽

        Rectangle rect = new Rectangle();

        rect.length = 5;

        rect.width = 3;

        // 输出面积

        System.out.println("The area of rectangle is " + rect.getArea());

    }

}

```

输出结果：

```

The area of rectangle is 15

```

7. 继承和多态

```java

// 父类

class Animal {

    public void sound() {

        System.out.println("The animal makes a sound");

    }

}

// 子类

class Dog extends Animal {

    public void sound() {

        System.out.println("The dog says woof");

    }

}

// 子类

class Cat extends Animal {

    public void sound() {

        System.out.println("The cat says meow");

    }

}

// 测试类

public class AnimalSound {

    public static void main(String[] args) {

        // 创建Animal、Dog、Cat对象并调用sound方法

        Animal animal = new Animal();

        Dog dog = new Dog();

        Cat cat = new Cat();

        animal.sound(); // 输出 "The animal makes a sound"

        dog.sound();    // 输出 "The dog says woof"

        cat.sound();    // 输出 "The cat says meow"

        // 多态：Animal类型的变量可以引用Dog、Cat对象并调用sound方法

        Animal ani1 = new Dog();

        Animal ani2 = new Cat();

        ani1.sound();   // 输出 "The dog says woof"

        ani2.sound();   // 输出 "The cat says meow"

    }

}

```

输出结果：

```

The animal makes a sound

The dog says woof

The cat says meow

The dog says woof

The cat says meow

```

8. 接口和实现

```java

// 接口

interface Shape {

    public void draw();

    public double getArea();

}

// 实现类

class Rectangle implements Shape {

    private int length;

    private int width;

    public Rectangle(int length, int width) {

        this.length = length;

        this.width = width;

    }

    public void draw() {

        System.out.println("Drawing a rectangle");

    }

    public double getArea() {

        return length * width;

    }

}

// 实现类

class Circle implements Shape {

    private int radius;

    public Circle(int radius) {

        this.radius = radius;

    }

    public void draw() {

        System.out.println("Drawing a circle");

    }

    public double getArea() {

        return Math.PI * radius * radius;

    }

}

// 测试类

public class ShapeTest {

    public static void main(String[] args) {

        // 创建Rectangle、Circle对象并调用draw、getArea方法

        Rectangle rect = new Rectangle(5, 3);

        Circle circle = new Circle(2);

        rect.draw();    // 输出 "Drawing a rectangle"

        System.out.println("The area of the rectangle is " + rect.getArea());  // 输出 "The area of the rectangle is 15.0"

        circle.draw();  // 输出 "Drawing a circle"

        System.out.println("The area of the circle is " + circle.getArea());    // 输出 "The area of the circle is 12.566370614359172"

    }

}

```

输出结果：

```

Drawing a rectangle

The area of the rectangle is 15.0

Drawing a circle

The area of the circle is 12.566370614359172

```

9. 异常处理

```java

import java.util.Scanner;

public class Divide {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the dividend: ");

        int dividend = scanner.nextInt();

        System.out.print("Enter the divisor: ");

        int divisor = scanner.nextInt();

        try {

            int quotient = dividend / divisor;

            System.out.println(dividend + " / " + divisor + " = " + quotient);

        } catch (ArithmeticException e) {

            System.out.println("Error: division by zero!");

        } finally {

            scanner.close();

        }

    }

}

```

输出结果：

```

Enter the dividend: 10

Enter the divisor: 2

10 / 2 = 5

```

或者

```

Enter the dividend: 10

Enter the divisor: 0

Error: division by zero!

```

10. 文件读写

```java

import java.io.File;

import java.io.FileWriter;

import java.io.IOException;

import java.util.Scanner;

public class FileInOut {

    public static void main(String[] args) {

        // 写入文件

        try {

            // 创建或打开文件

            File file = new File("output.txt");

            FileWriter writer = new FileWriter(file);

            // 写入字符串

            writer.write("Hello world!\n");

            writer.write("This is a test file.\n");

            // 关闭文件

            writer.close();

        } catch (IOException e) {

            System.out.println("Error writing file!");

        }

        // 读取文件

        try {

            // 打开文件

            File file = new File("output.txt");

            Scanner scanner = new Scanner(file);

            // 逐行读取并输出到控制台

            while (scanner.hasNextLine()) {

                System.out.println(scanner.nextLine());

            }

            // 关闭文件

            scanner.close();

        } catch (IOException e) {

            System.out.println("Error reading file!");

        }

    }

}

```

输出结果：

```

Hello world!

This is a test file.

```