Java复习

1．初始化方法

public class HelloWorld {

String name; // 声明变量name

String sex; // 声明变量sex

static int age;// 声明静态变量age

// 构造方法

public HelloWorld () {

System.out.println("通过构造方法初始化name");

name = "tom";

}

// 初始化块

{

System.out.println("通过初始化块初始化sex");

sex = "男";

}

// 静态初始化块

static {

System.out.println("通过静态初始化块初始化age");

age = 20;

}

public void show() {

System.out.println("姓名：" + name + "，性别：" + sex + "，年龄：" + age);

}

public static void main(String[] args) {

// 创建对象

HelloWorld hello = new HelloWorld();

// 调用对象的show方法

hello.show();

}

}

2.基本类型转换

基本类型转换为字符串

int c=10；

String str1=Integer.toString(c);

String str2=String.valueOf(c);

字符串转换为基本类型

String str=”8”;

int d=Integer.parseInt(str);

int e=Integer.valueOf(str);

String 转换为float

float f1=Float.parseFloat(str);

String ss = Long.toString(a); //long到string型

char[] ch = ss.toCharArray(); //string到char[]数组

System.out.println("请输入一个字符串：");

String str = s.nextLine(); //字符串的输入

String temp = null; //字符串为空

String str = str1+str2;//字符串连接

猜生日游戏

import javax.swing.JOptionPane;

publicclass GuessBirthDateUsingConfirmationDialog {

publicstaticvoid main(String[] args) {

String set1 = " 1 3 5 7\n" + " 9 11 13 15\n" + "17 19 21 23\n"

+ "25 27 29 31";

String set2 = " 2 3 6 7\n" + "10 11 14 15\n" + "18 19 22 23\n"

+ "26 27 30 31";

String set3 = " 4 5 6 7\n" + "12 13 14 15\n" + "20 21 22 23\n"

+ "28 29 30 31";

String set4 = " 8 9 10 11\n" + "12 13 14 15\n" + "24 25 26 27\n"

+ "28 29 30 31";

String set5 = "16 17 18 19\n" + "20 21 22 23\n" + "24 25 26 27\n"

+ "28 29 30 31";

int date = 0;

// Prompt the user to answer questions，提示内容

int answer = JOptionPane.showConfirmDialog(null,

"Is your birthdate in these numbers?\n" + set1);

if (answer == JOptionPane.YES_OPTION)

date += 1;

answer = JOptionPane.showConfirmDialog(null,

"Is your birthdate in these numbers?\n" + set2);

if (answer == JOptionPane.YES_OPTION)

date += 2;

answer = JOptionPane.showConfirmDialog(null,

"Is your birthdate in these numbers?\n" + set3);

if (answer == JOptionPane.YES_OPTION)

date += 4;

answer = JOptionPane.showConfirmDialog(null,

"Is your birthdate in these numbers?\n" + set4);

if (answer == JOptionPane.YES_OPTION)

date += 8;

answer = JOptionPane.showConfirmDialog(null,

"Is your birthdate in these numbers?\n" + set5);

if (answer == JOptionPane.YES_OPTION)

date += 16;

JOptionPane.showMessageDialog(null, "Your birthdate is "+ date + "!");

}

}

产生随机数:

(int)( Math.random()*10)

double x=Math.random()*2-1;//-1到1

输入：

1.Scanner input=new Scanner(System.in);

2.int number=input.nextInt();

符号

&&与

||或

System.out.println("Is " + number+ " divisible by 2 or 3, but not both? "

+ ((number % 2 == 0) ^ (number % 3 == 0)));

}

乘法表

publicclass MultiplicationTable {

/** Main method */

publicstaticvoid main(String[] args) {

// Display the table heading

System.out.println(" Multiplication Table");

// Display the number title

System.out.print(" ");

for (int j = 1; j<= 9; j++)

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

System.out.println("\n-----------------------------------------");

// Print table body

for (int i = 1; i<= 9; i++) {

System.out.print(i + " | ");

for (int j = 1; j<= 9; j++) {

// Display the product and align properly

System.out.printf("%4d", i * j);

}

System.out.println();

}

}

}

循环 while比if好用

While(执行的条件：){

循环体；

}

Sort();//排序

求和：

publicstaticvoid main(String[] args) {

int sum = 0;

// Keep reading data until the user answers No

int option = 0;

while (option == JOptionPane.YES_OPTION) {

// Read the next data

String dataString = JOptionPane

.showInputDialog("Enter an int value: ");

int data = Integer.parseInt(dataString);

sum += data;

option = JOptionPane.showConfirmDialog(null, "Continue?");

}

JOptionPane.showMessageDialog(null, "The sum is " + sum);

}

Sqrt()//开根号

Abs()//绝对值

图形界面

建立按钮

JButtonjbtOK=new JButton(“内容”);

建立面板

JPanel panel=new JPanel();

Panel.add(jbtOK)//添加按钮