JAVA语法基础总结

package com.chunchuner.fourcompute;
import java.util.Random;
public class Arithmatics {
private static Random random = new Random();
private final static int COUNT = 30;

private static boolean getProject() {
    int num1 = random.nextInt(101);
    int num2 = random.nextInt(101);
    int index = random.nextInt(4);
    String str = "";
    boolean flag = false;
    int answer = 0;
    switch (index) {
    case 0:
        answer = num1 + num2;
        if (answer > 100) {
            break;
        }
        str = num1 + "+" + num2 + "=";
        flag = true;
        break;
    case 1:
        if (num1 < num2) {
            break;
        }
        str = num1 + "-" + num2 + "=";
        flag = true;
        break;
    case 2:
        answer = num1 * num2;
        if (answer > 100) {
            break;
        }
        str = num1 + "*" + num2 + "=";
        flag = true;
        break;
    case 3:
        if (num2 == 0) {
            break;
        }
        str = num1 + "÷" + num2 + "=";
        flag = true;
        break;
    }
    if (flag) {
        System.out.println(str);
    }
    return flag;
}
public static void main(String[] args) {
    System.out.println("");
    int count = 0;
    do {
        if (getProject()) {
            count++;
        }
    } while (count < COUNT);
}

}
结果：
17÷39=
99-40=
0+87=
80÷93=
51-40=
59÷21=
4+66=
1÷62=
49+30=
86÷8=
54÷20=
36+29=
53-11=
46-1=
27*1=
12+80=
49-22=
6+23=
37+54=
98÷76=
77-17=
42+35=
64+16=
77+18=
14+14=
79÷8=
95-23=
77+13=
37+16=
43÷86=

// An addition program

import javax.swing.JOptionPane; // import class JOptionPane

public class Addition {
public static void main( String args[] )
{
String firstNumber, // first string entered by user
secondNumber; // second string entered by user
int number1, // first number to add
number2, // second number to add
sum; // sum of number1 and number2

  // read in first number from user as a string
  firstNumber =
     JOptionPane.showInputDialog( "Enter first integer" );

  // read in second number from user as a string
  secondNumber =
     JOptionPane.showInputDialog( "Enter second integer" );

  // convert numbers from type String to type int
  number1 = Integer.parseInt( firstNumber ); 
  number2 = Integer.parseInt( secondNumber );

  // add the numbers
  sum = number1 + number2;

  // display the results
  JOptionPane.showMessageDialog(
     null, "The sum is " + sum, "Results",
     JOptionPane.PLAIN_MESSAGE );

  System.exit( 0 );   // terminate the program

}
}

public class EnumTest {

public static void main(String[] args) {
	Size s=Size.SMALL;
	Size t=Size.LARGE;
	//s和t引用同一个对象？
	System.out.println(s==t);  //
	//是原始数据类型吗？
	System.out.println(s.getClass().isPrimitive());
	//从字符串中转换
	Size u=Size.valueOf("SMALL");
	System.out.println(s==u);  //true
	//列出它的所有值
	for(Size value:Size.values()){
		System.out.println(value);
	}
}

}
enum Size{SMALL,MEDIUM,LARGE};

false
false
true
SMALL
MEDIUM
LARGE

/**
@version 1.10 2004-02-10
@author Cay Horstmann
*/

import java.util.*;

public class InputTest
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);

  // get first input
  System.out.print("What is your name? ");
  String name = in.nextLine();

  // get second input
  System.out.print("How old are you? ");
  int age = in.nextInt();
  
  
/* int i;
 String value="100";
 i=Integer.parseInt(value);
 i=200;
 String s=String.valueOf(i);*/
 
  // display output on console
  System.out.println("Hello, " + name + ". Next year, you'll be " + (age + 1));

}
}

What is your name? 1
How old are you? 32
Hello, 1. Next year, you'll be 33

public class RandomStr
{
public static void main(String[] args)
{
//定义一个空字符串
String result = "";
//进行6次循环
for(int i = 0 ; i < 6 ; i ++)
{
//生成一个97～122的int型的整数
int intVal = (int)(Math.random() * 26 + 97);
//将intValue强制转换为char后连接到result后面
result = result + (char)intVal;
}
//输出随机字符串
System.out.println(result);
}
}
cjfkbe

// Drawing shapes
import java.awt.Graphics;
import javax.swing.*;

public class SwitchTest extends JApplet {
int choice;

public void init()
{
String input;

  input = JOptionPane.showInputDialog( 
             "Enter 1 to draw lines\n" +
             "Enter 2 to draw rectangles\n" +
             "Enter 3 to draw ovals\n" );

  choice = Integer.parseInt( input );

}

public void paint( Graphics g )
{
for ( int i = 0; i < 10; i++ ) {
switch( choice ) {
case 1:
g.drawLine( 10, 10, 250, 10 + i * 10 );
break;
case 2:
g.drawRect( 10 + i * 10, 10 + i * 10,
50 + i * 10, 50 + i * 10 );
break;
case 3:
g.drawOval( 10 + i * 10, 10 + i * 10,
50 + i * 10, 50 + i * 10 );
break;
default:
JOptionPane.showMessageDialog(
null, "Invalid value entered" );
} // end switch
} // end for
} // end paint()
} // end class SwitchTest

import java.math.BigDecimal;

public class TestBigDecimal
{
public static void main(String[] args)
{
BigDecimal f1 = new BigDecimal("0.05");
BigDecimal f2 = BigDecimal.valueOf(0.01);
BigDecimal f3 = new BigDecimal(0.05);
System.out.println("下面使用String作为BigDecimal构造器参数的计算结果：");
System.out.println("0.05 + 0.01 = " + f1.add(f2));
System.out.println("0.05 - 0.01 = " + f1.subtract(f2));
System.out.println("0.05 * 0.01 = " + f1.multiply(f2));
System.out.println("0.05 / 0.01 = " + f1.divide(f2));
System.out.println("下面使用double作为BigDecimal构造器参数的计算结果：");
System.out.println("0.05 + 0.01 = " + f3.add(f2));
System.out.println("0.05 - 0.01 = " + f3.subtract(f2));
System.out.println("0.05 * 0.01 = " + f3.multiply(f2));
System.out.println("0.05 / 0.01 = " + f3.divide(f2));
}
}
下面使用String作为BigDecimal构造器参数的计算结果：
0.05 + 0.01 = 0.06
0.05 - 0.01 = 0.04
0.05 * 0.01 = 0.0005
0.05 / 0.01 = 5
下面使用double作为BigDecimal构造器参数的计算结果：
0.05 + 0.01 = 0.06000000000000000277555756156289135105907917022705078125
0.05 - 0.01 = 0.04000000000000000277555756156289135105907917022705078125
0.05 * 0.01 = 0.0005000000000000000277555756156289135105907917022705078125
0.05 / 0.01 = 5.000000000000000277555756156289135105907917022705078125