1 Welcome to java

public class ch01Welcome {

    public static void main(String[] args) {

        System.out.println("Welcome to Java!"); //运行的快捷键为crtl + F11

    }

}

2 从控制台输入

package cn.jxufe.java;

import java.util.Scanner;

public class ch02ConsoleInput {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input = new Scanner(System.in);

        System.out.println("enter a number for radius: ");

        double radius = input.nextDouble();

        double area = radius * radius * 3.14159;

        System.out.println("the area for the circle of radius " + radius + " is " + area);

    }

}

输入三个数，计算三个数的平均值：

package cn.jxufe.java;

import java.util.Scanner;

import jdk.nashorn.internal.objects.NativeUint16Array;

public class ch03ComputerAverage {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input = new Scanner(System.in);

        System.out.print(" Enter three numbers : ");

        double number1 = input.nextDouble();

        double number2 = input.nextDouble();

        double number3 = input.nextDouble();

        double average = (number1 + number2 + number3) / 3;

        System.out.println("the average of " + number1 + " " + number2 + " " + number3 + " is " + average);

    }

}

3 产生随机数

package cn.jxufe.java;

import java.util.Scanner;

public class ch04RanomNumber {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        int number1 = (int) (Math.random() * 10);

        int number2 = (int) (Math.random() * 10);

        if (number1 < number2) {

            int temp = number1;

            number1 = number2;

            number2 = temp;

        }

        System.out.println("what is " + number1 + " - " + number2 + " ?");

        Scanner input = new Scanner(System.in);

        int answer = input.nextInt();

        if (number1 - number2 == answer)

            System.out.println("you are right");

        else {

            System.out.println("you are wrong");

            System.out.println(number1 + " - " + number2 + " should be " + (number1 - number2));

        }

    }

}

4 数学函数

4.1 三角函数

4.2 指数函数

4.3 取整方法

4.4 min、max和abs方法

4.5 random方法

5 String类型

5.1 求字符串长度、从字符串中获取字符、连接字符串和字符串大小写转换

package cn.jxufe.java;

public class ch05StringType {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        String message = "Welcome to Java";

        System.out.println("the length of " + message + " is " + message.length()); // 求字符串长度

        System.out.println(message.charAt(0)); // 从字符串中获取字符

        System.out.println(message.concat(" and python")); // 连接字符串

        System.out.println(message + " and python");

        System.out.println(message.toLowerCase()); // 字符串大小写转换

        System.out.println(message.toUpperCase());

    }

}

5.2 从控制台读取字符串

package cn.jxufe.java;

import java.util.Scanner;

public class ch05StringType {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input = new Scanner(System.in);

        System.out.println("enter three words separated by spaces");

        String s1 = input.next();

        String s2 = input.next();

        String s3 = input.next();

        System.out.println("s1 is " + s1);

        System.out.println("s2 is " + s2);

        System.out.println("s3 is " + s3);

        System.out.println("enter a line: ");

        Scanner input2 = new Scanner(System.in);

        String s= input2.nextLine();

        System.out.println("the line entered is " + s);

    }

}

5.3 从控制台读取字符

package cn.jxufe.java;

import java.util.Scanner;

public class ch06ReadChar {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input = new Scanner(System.in);

        System.out.println("enter a character: ");

        String s = input.nextLine();

        char ch = s.charAt(0);

        System.out.println("the character entered is " + ch);

    }

}

5.4 字符串比较

package cn.jxufe.java;

public class ch07StringCompare {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        String s1 = "Welcome to java ";

        String s2 = "Welcome to java ";

        String s3 = "Welcome to python ";

        System.out.println(s1.equals(s2)); // 内容相等

        System.out.println(s1.equals(s3));

        System.out.println(s1.compareTo(s2)); // 从左至右第一个不同字符之间的距离

        System.out.println(s1.compareTo(s3));

        System.out.println(s1.startsWith("Wel")); // 字符串检测

        System.out.println(s1.endsWith("va"));

        System.out.println(s1.contains("to"));

    }

}

5.5 获取字符串中的字符或者子串

package cn.jxufe.java;

import sun.print.resources.serviceui;

public class ch08subString {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        String s = "Welcome to java";

        System.out.println(s.indexOf('W'));

        System.out.println(s.indexOf('o'));

        System.out.println(s.indexOf("to"));

        System.out.println(s.indexOf("To"));

        System.out.println();

        System.out.println(s.lastIndexOf('W'));

        System.out.println(s.lastIndexOf('o'));

        System.out.println(s.lastIndexOf("to"));

        System.out.println(s.lastIndexOf("To"));

    }

}

6 方法重载

package cn.jxufe.java;

import com.sun.org.apache.regexp.internal.recompile;

public class ch09OverLoading {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        System.out.println("the maximum of 3 and 4 is " + max(3, 4));

        System.out.println("the maximum of 3.0 and 5.4 is " + max(3, 5.4));

        System.out.println("the maximum of 3.0, 5.4 and 10.14 is " + max(3, 5.4, 10.14));

    }

    public static int max(int num1, int num2) {

        return Math.max(num1, num2);

    }

    public static double max(double num1, double num2) {

        return Math.max(num1, num2);

    }

    public static double max(double num1, double num2, double num3) {

        return max(max(num1, num2), num3);

    }

}

7 foreach循环

package cn.jxufe.java;

public class ch10ForEach {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        double[] myList = { 1.9, 2.9, 3.4, 3.5 };

        for (double e : myList) {

            System.out.print(e + " ");

        }

    }

}

8 应用一维数组分析数字

找出一些数中大于平均值的个数。让用户给出数据的个数和输入的数据。

package cn.jxufe.java;

import java.util.Scanner;

public class ch11AnalyzeNumber {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input = new Scanner(System.in);

        System.out.println("enter the number of items: ");

        int n = input.nextInt();

        double[] numbers = new double[n];

        double sum = 0;

        System.out.println("enter the numbers: ");

        for (int i = 0; i < n; i++) {

            numbers[i] = input.nextDouble();

            sum += numbers[i];

        }

        double average = sum / n;

        int count = 0;

        for (double e : numbers) {

            if (e > average)

                count++;

        }

        System.out.println("average is " + average);

        System.out.println("number of elements above the average is " + count);

    }

}

9 一维数组的复制

package cn.jxufe.java;

public class ch12Arraycopy {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        double[] myList = { 1.9, 2.9, 3.4, 3.5 };

        double[] newList = new double[myList.length];

        System.arraycopy(myList, 0, newList, 0, myList.length);

        for(double e:newList)

            System.out.print(e + " ");

    }

}

10 将一维数组传递给方法

package cn.jxufe.java;

public class ch13ArrayTest {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        int x = 1;

        int[] y = new int[10];

        m(x, y);

        System.out.println("x is " + x);

        System.out.println("y[0] is " + y[0]);

    }

    public static void m(int number, int[] numbers) {

        number = 1001;

        numbers[0] = 5555;

    }

}

11 可变长参数列表

package cn.jxufe.java;

public class ch14VarArgsDemo {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        printMax(34, 3, 3, 2, 56.5);

        printMax(new double[] { 1, 2, 3 }); // 匿名数组

    }

    public static void printMax(double... numbers) {

        if (numbers.length == 0) {

            System.out.println("no argument passed ");

            return;

        }

        double result = numbers[0];

        for (double e : numbers) {

            if (e > result)

                result = e;

        }

        System.out.println("the max value is " + result);

    }

}

12 Arrays类

package cn.jxufe.java;

import java.util.Arrays;

public class ch15ArraysDemo {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        double[] numbers = { 6.0, 4.4, 1.9, 2.9, 3.4, 3.5 };

        Arrays.sort(numbers);

        System.out.println(Arrays.toString(numbers)); // 打印一维数组的简单方法

        int[] list = { 2, 4, 7, 10, 11, 45 };

        System.out.println(" 11 index is " + Arrays.binarySearch(list, 11));

        int[] list2 = { 2, 3, 5, 1 };

        Arrays.fill(list2, 5);

        System.out.println(Arrays.toString(list2));

    }

}

13 将二维数组传递给方法

package cn.jxufe.java;

import java.util.Arrays;

import java.util.Scanner;

public class ch16TowDimensionArray {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        int[][] m = getArray();

        System.out.println(Arrays.deepToString(m)); // 打印二维数组的简单方法

        System.out.println("Sumof all element is " + sum(m));

    }

    public static int[][] getArray() {

        Scanner input = new Scanner(System.in);

        int[][] m = new int[3][4];

        System.out.println("enter " + m.length + " rows and " + m[0].length + " columns: ");

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

            for (int j = 0; j < m[i].length; j++)

                m[i][j] = input.nextInt();

        }

        return m;

    }

    public static int sum(int[][] m) {

        int total = 0;

        for (int row = 0; row < m.length; row++) {

            for (int column = 0; column < m[row].length; column++) {

                total += m[row][column];

            }

        }

        return total;

    }

}

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