JAVA入门基础代码

public static void main(String args[]){ int x=(int)(Math.random()*10); System.out.println("随机数 x 放大 10 倍后的整数值:"+x); switch(x){ case 0: System.out.println("case 0:"+x); break; case 1: System.out.println("case 1:"+x); break; default: System.out.println("default:"+x); break; }
} }
例 1-12 Menu.java class Menu{
public static void main(String args[]) throws java.io.IOException{ char choice; do{ System.out.println("Help on:"); System.out.println(" 1. if"); System.out.println(" 2. switch"); System.out.println(" 3. while"); System.out.println(" 4. do-while"); System.out.println(" 5. for\n"); System.out.println("Choose one:"); choice=(char)System.in.read(); } while(choice<'1'||choice>'5'); System.out.println("\n");
} }
例 1-3 DecisionDemo.java class DecisionDemo{
public static void main(String args[]){ short x=1,y=2,z; // 错误代码 // z = x + y; // 正确代码 z=(short)(x+y); System.out.println(z);
} }
例 1-14 BreakDemo.java class BreakDemo{
public static void main(String args[]){ int nSum=0; int nCounter=0; while(nCounter<=100){ if(nSum>2000) break; else{ nCounter++; nSum=nSum+nCounter; System.out.println("累加结果："+nSum); } }
} }
例 1-6 BasicMath.java class BasicMath{
public static void main(String args[]){ System.out.println("Integer Arithmetic"); int a=1+1; int b=a*3; int c=b/4; int d=c-a; System.out.println("c = "+c); System.out.println("d = "+d); System.out.println("\nFloating Point Arithmetic"); double da=1+1; double db=da*3; double dc=db/4; double dd=dc-a; System.out.println("dc = "+dc); System.out.println("dd = "+dd); int x = 42; double y = 42.25; System.out.println("x mod 10 = " + x % 10); System.out.println("y mod 10 = " + y % 10);
例 1-1 DoubleVariableDemo.java class DoubleVariableDemo{
public static void main(String args[]){ double dRadius=2.0d; double dArea=Math.PI*dRadius*dRadius; System.out.println("半径为 2 的圆的面积："+dArea);
} }
例 1-7 BooleanOperatorDemo.java class BooleanOperatorDemo{
public static void main(String args[]){ int nOperator1=5; int nOperator2=10; if((nOperator1>4)&&(nOperator2>9)) System.out.println("nOperator1 大于 4 并且 nOperator2 大于 9");
} }
例 1-4 IntegerConstantDemo . java class IntegerConstantDemo{
public static void main(String args[]){ final byte nMaxValue_1=100; final short nMaxValue_2=200; final int nMaxValue_3=300; final long nMaxValue_4=400; System.out.println("整数常量的 nMaxValue_1 值"+nMaxValue_1); System.out.println("整数常量的 nMaxValue_2 值"+nMaxValue_2); System.out.println("整数常量的 nMaxValue_3 值"+nMaxValue_3); System.out.println("整数常量的 nMaxValue_4 值"+nMaxValue_4); // nMaxValue_1 = nMaxValue_1 + 1; 不能更改常量的值
else System.out.println("逻辑关系判断不成立");
} }
例 1-8 BoolLogic.java
class BoolLogic{
public static void main(String args[]){
boolean a=true;
boolean b=false;
boolean c=a|b;
if(sex.equals("男")){ System.out.println("他的性别是男");
}else{ System.out.println("她的性别是女");
} System.out.println("我在学习控制语句"); } }
例 1-11 SwitchDemo.java class SwitchDemo{
switch(choice){ case '1': System.out.println("The if:\n"); System.out.println("if(condition) statement;"); System.out.println("else statement;"); break; case '2': System.out.println("The switch:\n"); System.out.println("switch(expression) {"); System.out.println(" case constant:"); System.out.println(" statement sequence"); System.out.println(" break;"); System.out.println(" // ..."); System.out.println("}"); break; case '3': System.out.println("The while:\n"); System.out.println("while(condition) statement;"); break; case '4': System.out.println("The do-while:\n"); System.out.println("do {"); System.out.println(" statement;"); System.out.println("} while (condition);"); break; case '5': System.out.println("The for:\n"); System.out.print("for(init; condition; iteration)"); System.out.println(" statement;"); break; } } }