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;    }}