package test2;

public class test2 {

public static void main(String[] args) {
// TODO Auto-generated method stub
int a = Integer.parseInt(args[0]);
int b = Integer.parseInt(args[1]);
System.out.println(a+"+"+b+"="+(a+b));
System.out.println(a+"-b"+"="+(a-b));
System.out.println(a+"*"+b+"="+(a*b));
System.out.println(a+"/"+b+"="+(a/b));


}

}

String next()以空格和回车结束

String nextLine（）回车结束

创建Scanner类的一个对象

Scanner scanner=new Scanner(System.in);

//scanner 是堆中的一个地址

 通过scanner调用next等方法，接收控制台输入的数据

　　　　System.out.println("姓名：")；

　　　　String name=scanner.next();

package test2;

import java.util.Scanner;

public class test18 {
/*
* zhangfei
* boy
* 22
* 1.99
* write program*/
public static void main(String[] args) {
//创建Scanner对象
Scanner scanner=new Scanner(System.in);
//像控制台输出文本
System.out.println("姓名:");
String name=scanner.next();
System.out.println("性别：");
char sex=scanner.next().charAt(1);
System.out.println("年龄：");
int age=scanner.nextInt();
System.out.println("身高");
double height=scanner.nextDouble();
System.out.println("爱好：");
String type=scanner.next();
System.out.println("大家好，我叫："+name+",今年："+age+"岁圣爱："+height+"米，我是"+type+sex+"士"
);
}

}

//char String.charAt(int index);从字符串中获取指定下标的字符，下表从0开始

ctrl+d  删除某一行   alt+/   补全代码  

类型Scanner声明的变量在栈空间  new出来的对象在堆空间

Scanner scanner=new Scanner（System.in）存放的是   堆空间中该对象的一个地址

可以调用scanner里的各种方法接收控制台输入

Scanner scanner=new Scanner(System.in);
String name=scanner.next();

package test2;

import java.util.Scanner;

public class test6 {

public static void main(String[] args) {
Scanner scanner=new Scanner(System.in);
System.out.println("java:");
int java=scanner.nextInt();
System.out.println("android:");
int android=scanner.nextInt();
System.out.println("sql:");
int sql=scanner.nextInt();
if(java>=android &&java>=sql)
{
System.out.println("max=java");
}
else if(android >=sql){
System.out.println("max=android");

}else{
System.out.println("max=sql");
}
}

}

法二：

package test2;

import java.util.Scanner;

public class test19 {

public static void main(String[] args) {
Scanner scanner=new Scanner(System.in);
System.out.println("java android sql:");
int java=scanner.nextInt();
int android=scanner.nextInt();
int sql=scanner.nextInt();
int maxscore=java;
if(maxscore<android){
maxscore=android;
}
if(maxscore<sql){
maxscore=sql;
}
System.out.println("maxscore="+maxscore);
}

}

stepping into these obsolete frames may be hazardons to the target virtual machine.

package test2;

import java.util.Scanner;

public class test2{
public static void main(String[] args){
Scanner scanner=new Scanner(System.in);
System.out.println("input month");
int month=scanner.nextInt();
switch(month){
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
System.out.println("31 days");
break;
case 2:
System.out.println("28 days");
break;
case 4:
case 6:
case 9:
case 11:
System.out.println("30 days");
break;
default:
System.out.println("wrong");
}

}
}

package test3;

public class testa {
public static void main(String[] args) {
int i=65;
while(i<=65+25){
System.out.println((char)i+":"+i);
i++;
}

}
}

package test3;

public class testa {
public static void main(String[] args) {
char c=‘A‘;
while(c<=‘Z‘){
System.out.println(c+":"+(int)c);
c++;
}
}
}

数组声明的两种方式

package test3;

public class ArrayDemo01 {
public static void main(String args[]){
int arrayDemo[];//数组名的第一个字母小写第二个字母大写
int[] core;
}
}

赋值的得到一个hello  new得到的是两个hello

==  比较地址  equals  比较内容

package test3;

public class ArrayDemo01 {
public static void main(String args[]){
String str ="jikexueyuan";
System.out.println(str.length());
char data[] = str.toCharArray();
for (int i = 0;i<data.length;i++){
System.out.println(data[i]+"");
}
}
}

多行注释 /*..........*/

 单行注释 //

 多行注释快捷键：Ctrl   +   /

package test3;

public class ArrayDemo01 {
public static void main(String args[]){
String str ="jikexueyuan";
// System.out.println(str.length());
// char data[] = str.toCharArray();
// for (int i = 0;i<data.length;i++){
// System.out.println(data[i]+"");
// }

byte bytes[] = str.getBytes();
for(int i= 0;i< bytes.length;i++){
System.out.println(new String(bytes)+"\t");

}
}
}

StringBuffer是一个操作类，必须实例化

package test3;

public class ArrayDemo01 {
public static void main(String args[]){
StringBuffer sb = new StringBuffer();
sb.append("jikexueyuan");
System.out.println(sb.toString());
tell(sb);
System.out.println(sb.toString());

}
public static void tell(StringBuffer s){
s.append("i love ji");
}
}

 string不可更改  stringbuffer可以更改

java