Java入门基础代码

例1-1 DoubleVariableDemo.javaclass 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1-2 BooleanConstantDemo.javaclass BooleanConstantDemo{public static void main(String args[]){final boolean BFLAG=true;if(BFLAG)System.out.println("Always Print Out Me!");elseSystem.out.println("Never Print Out Me!");}}例1-3 DecisionDemo.javaclass 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1-4 IntegerConstantDemo . javaclass 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}}例1-5 DataConversionDemo.javaclass DataConversionDemo{public static void main(String args[]){int nOp1=2;float fOp2=2.25f;float fResult=nOp1*fOp2;System.out.println("混合运算结果："+fResult);}}例1-6 BasicMath.javaclass 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1-7 BooleanOperatorDemo.javaclass 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");elseSystem.out.println("逻辑关系判断不成立");}}例1-8 BoolLogic.javaclass BoolLogic{public static void main(String args[]){boolean a=true;boolean b=false;boolean c=a|b;boolean d=a&b;boolean e=a^b;boolean f=(!a&b)|(a&!b);System.out.println(" a|b = "+c);System.out.println(" a&b = "+d);System.out.println(" a^b = "+e);System.out.println("!a&b|a&!b = "+f);}}例1-9 MultByTwo.javaclass MultByTwo{public static void main(String args[]){int i;int num=0xFFFFFFE;for(i=0;i<4;i++){num=num<<1;System.out.println(num);}}}例1-10 IfElseStudy.javapublic class IfElseStudy{public static void main(String args[]){int age=65;String sex;sex=new String("男");if(age>60){System.out.println("他是老年人");}else{System.out.println("他不是老年人");}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.javaclass SwitchDemo{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.javaclass 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");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;}}}例1-13 ForDemo.javaclass ForDemo{public static void main(String args[]){int nSum,nCounter;for(nCounter=0,nSum=0;nCounter<=100;nCounter++){ nSum=nSum+nCounter;}System.out.println("100以内自然数的和为："+nSum);}}例1-14 BreakDemo.javaclass 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1-15 Break.javaclass Break{public static void main(String args[]){boolean t=true;first:{second:{third:{System.out.println("Before the break.");if(t)break second;System.out.println("This won't execute");}System.out.println("This won't execute");}System.out.println("This is after second block.");}}}例1-16 ContinueLabel.javaclass ContinueLabel{public static void main(String args[]){outer:for(int i=0;i<10;i++){for(int j=0;j<10;j++){if(j>i){System.out.println();continue outer;}System.out.print(" "+(i*j));}}System.out.println();}}例1-17 UseMethod.javaclass B{int i,j;B(int a,int b){i=a;j=b;}B(int a){i=a;j=a;}void show(String a){System.out.println(a);}int show(int c){System.out.println(c);}}class UseMethod{public static void main(String args[]){B subOb=new B(1,2);B subOc=new B(1);subOb.show("hello");subOc.show(12);}}例1-18 ExtendsDemo.javaclass Parent{public int x;public int doSomething(){return x*x;}public int doOtherthing(){return x;}}class Child extends Parent{int x;Child(int x){this.x=x;}public int doSomething(){return x=x*x*x;}}public class ExtendsDemo{public static void main(String args[]){ int nResult;Parent parent=new Parent();parent.x=2;Child child=new Child(3);nResult=parent.doSomething();System.out.println("调用父类中的被覆盖方法："+nResult);nResult=child.doSomething();System.out.println("调用子类中的覆盖方法："+nResult);nResult=parent.doOtherthing();System.out.println("调用父类中没有被覆盖的方法："+nResult);}}例1-19 UseSuper.javaclass A{int i;}class B extends A{int i;B(int a,int b){super.i=a;i=b;}void show(){System.out.println("i in superclass: "+super.i);System.out.println("i in subclass: "+i);}}class C extends B{int j;C(int a,int b,int c){super(a,b);j=c;}void show(){System.out.println(j);}}class UseSuper{public static void main(String args[]){B subOb=new B(1,2);C subOc=new C(1,3,4);subOb=subOc;System.out.println(subOb.i);// System.out.println(subOb.j); 错误代码subOb.show();}}例1-20 Package.javapackage mypackage;public class Package{int a=1;private int b=2;protected int c=3;public int d=4;public Package(){System.out.println("base constructor");System.out.println("n = "+a);System.out.println("n_pri = "+b);System.out.println("n_pro = "+c);System.out.println("n_pub = "+d);}}例1-21 InterfaceExample.javainterface Charge{public void charge();}class Bus implements Charge{public void charge(){System.out.println("公共汽车:一元二角/张,不计算公里数");}}class Cinema implements Charge{public void charge(){System.out.println("电影院:门票,二十元/张");}}class InterfaceExample{public static void main(String args[]){ Bus 二路汽车=new Bus ();Cinema 环艺=new Cinema ();二路汽车.收取费用();环艺.收取费用();}}。