运算符
比较运算符
比较的结果boolean
大于>
大于等于>=
小于<
小于等于<=
等于==
不等于 ! ==
逻辑运算符
单于&
双与&& 有假则假 同真则真
或 |
双或 | | 有真则真 同假则假
非 !
异或^
单与和双与的区别:
单与 & 全部执行 再将结果进行逻辑运算
双与 && 如果第一个条件为假 则后面的条件无论真假结果都是假 所以 后面的条件不运行
单或和双或的区别
单或 | 全部执行 再将结果进行逻辑运算
双或 || 如果第一个条件为真 则后面的条件无论真假结果都是真 所以 后面的条件不运行
if语句
单 if
单if语句
… A
if(条件){
如果条件为真时,执行的语句 B
}
… C
条件为真 A->B->C
条件为假 A->C
if-else分支
if-else分支
… A
if(条件){
如果条件为真时,执行的语句 B
}else{
如果条件为假时,执行的语句 C
}
… D
条件为真时:A->B->D
条件为假时:A->C->D
多if-else嵌套
if-else嵌套
… A
if(条件1){
条件1为真… B
if(条件2){
条件2为真… B1
}else{
条件2为假… B2
}
… B3
}else{
条件1为假… C
}
… D
条件1为真 且 条件2为真:A->B->B1->B3->D
条件1为真 且 条件2为假:A->B->B2->B3->D
条件1为假 A->C->D
多if-else分支
多if-else分支
…A
if(条件1){ > < >= <= == !=
条件1为真…B
}else if(条件2){
条件2为真…C
}else if(条件3){
条件3为真…D
}else{
… E
}
…F
条件1为真:A->B->F
条件1为假,条件2位真:A->C->F
条件1为假,条件2位假,条件3为真:A->D->F
三者都为假:A->E->F
switch语句
选择语句switch
switch(变量){
case 选项1:
如果变量= =选项1执行的语句
break;
case 选项2:
如果变量==选项2执行的语句
break;
…
default:
如果选项n中没有适合变量的值,则执行
break;
}
if与switch的区别
if可以对区间值进行比较 也可以对固定值进行比较
switch只能对固定的一个值进行比较 推荐
布尔表达式
布尔表达式(条件表达式)(三目运算)
数据类型 变量名=布尔表达式?常量值1:常量值2;
true 输出常量1
false 输出常量2
编程题
import java.util.Scanner;
public class Demo3_1{
public static void main(String[] args){
//1.提示用户输入a,b,c
Scanner scanner=new Scanner(System.in);
System.out.print("Enter a,b,c:");
double a=scanner.nextDouble();
double b=scanner.nextDouble();
double c=scanner.nextDouble();
//2.计算判别式
double delt=Math.pow(b,2)-4*a*c;
//3.判断判别式,输出根
if(delt>0){
double r1=(-b+Math.sqrt(delt))/2*a;
double r2=(-b-Math.sqrt(delt))/2*a;
System.out.println("The equation has two roots "+r1+"and"+r2);
}else if(delt==0){
double r=-b/2*a;
System.out.println("The equation has one root"+r);
}else{
System.out.println("The equation has no real roots");
}
}
}
import java.util.Scanner;
public class Demo3_2 {
public static void main(String[] args) {
//1.输入a,b,c,d,e,f
Scanner scanner=new Scanner(System.in);
System.out.print("Enter a,b,c,d,e,f:");
double a=scanner.nextDouble();
double b=scanner.nextDouble();
double c=scanner.nextDouble();
double d=scanner.nextDouble();
double e=scanner.nextDouble();
double f=scanner.nextDouble();
//2.计算ad-bc及x,y的值
double delt=a*d-b*c;
//3.判断
if(delt==0){
System.out.println("The equation has no solution");
}else{
double x=(e*d-b*f)/(a*d-b*c);
double y=(a*f-e*c)/(a*d-b*c);
System.out.println("x is "+x+" and y is "+y);
}
}
}
import java.util.Scanner;
public class Demo3_3 {
public static void main(String[] args) {
//1.输入今天的日期数和今天之后的天数
Scanner scanner=new Scanner(System.in);
System.out.print("Enter today's day:");
int today=scanner.nextInt();
System.out.print("Enter the number of days elapsed since today:");
int days=scanner.nextInt();
//2.计算日期
int number=(days+today)%7;
//3.判断并输出
switch(today){
case 0:
System.out.print("Today is Sunday");
break;
case 1:
System.out.print("Today is Monday");
break;
case 2:
System.out.print("Today is Tuesday");
break;
case 3:
System.out.print("Today is Wednesday");
break;
case 4:
System.out.print("Today is Thursday");
break;
case 5:
System.out.print("Today is Friday");
break;
case 6:
System.out.print("Today is Saturday");
break;
}
switch(number){
case 0:
System.out.println(" and the future day is Sunday");
break;
case 1:
System.out.println(" and the future day is Monday");
break;
case 2:
System.out.println(" and the future day is Tuesday");
break;
case 3:
System.out.println(" and the future day is Wednesday");
break;
case 4:
System.out.println(" and the future day is Thursday");
break;
case 5:
System.out.println(" and the future day is Friday");
break;
case 6:
System.out.println(" and the future day is Saturday");
break;
}
}
}
3.4
import java.util.Scanner;
public class Demo3_4 {
public static void main(String[] args){
//1.输入一个九位编号
Scanner scanner=new Scanner(System.in);
System.out.print("Enter the first 9 digits of an ISBN as integer:");
int digit=scanner.nextInt();
int digitOri=digit;
//2.将九位编号分别取出
int d9=digit%10;
digit/=10;
int d8=digit%10;
digit/=10;
int d7=digit%10;
digit/=10;
int d6=digit%10;
digit/=10;
int d5=digit%10;
digit/=10;
int d4=digit%10;
digit/=10;
int d3=digit%10;
digit/=10;
int d2=digit%10;
digit/=10;
int d1=digit%10;
digit/=10;
//3.计算校验和
int d10=(d1*1+d2*2+d3*3+d4*4+d5*5+d6*6+d7*7+d8*8+d9*9)%11;
if(d10==10){
System.out.println("The ISBN-10 Number is "+d1+d2+d3+d4+d5+d6+d7+d8+d9+"X");
}else{
System.out.println("The ISBN-10 Number is "+d1+d2+d3+d4+d5+d6+d7+d8+d9+d10);
}
}
}
import java.util.Scanner;
public class Demo3_5 {
public static void main(String[] args) {
//1.用户输入整数
Scanner scanner=new Scanner(System.in);
System.out.print("Enter a three-digit integer:");
int digit=scanner.nextInt();
//2.拆分三位数
int a=digit%10;
int b=digit/100;
//3.对比个位和百位判断是否回文
if(a==b){
System.out.print("是回文数字");
}else{
System.out.print("不是回文数字!");
}
}
}
import java.util.Random;
import java.util.Scanner;
public class Demo3_6 {
public static void main(String[] args) {
//1.用户输入数
Scanner scanner=new Scanner(System.in);
System.out.print("scissor(0),rock(1),paper(2):");
int number=scanner.nextInt();
//电脑生成一个0~3的数
/*int c=(int)Math.random()*3;
*
* */
Random random=new Random();
int result=random.nextInt(3);
//2.比较输赢,输出结果
if(result==0&&number==0){
System.out.print("The computer is scissor.You are scissor too.It is a draw");
}else if(result==0&&number==1){
System.out.print("The computer is scissor.You are rock.You lose");
}else if(result==0&&number==2){
System.out.print("The computer is scissor.You are paper.You win");
}else if(result==1&&number==1){
System.out.print("The computer is rock.You are rock too.It is a draw");
}else if(result==1&&number==0){
System.out.print("The computer is rock.You are scissor.You lose");
}else if(result==1&&number==2){
System.out.print("The computer is rock.You are paper.You win");
}else if(result==2&&number==2){
System.out.print("The computer is paper.You are paper too.It is a draw");
}else if(result==2&&number==1){
System.out.print("The computer is paper.You are rock.You lose");
}else if(result==2&&number==0){
System.out.print("The computer is paper.You are scissor.You win");
}
}
}
import java.util.Scanner;
public class Demo3_7 {
public static void main(String[] args) {
//1.输入三角形的三边
Scanner scanner=new Scanner(System.in);
System.out.print("输入三角形三边长a,b,c:");
double a=scanner.nextDouble();
double b=scanner.nextDouble();
double c=scanner.nextDouble();
//2. 判断输入值是否合法
if(a+b<=c||a+c<=b||b+c<=a){
System.out.println("输入值不合法");
}else{
double l=a+b+c;
System.out.println("输入值合法,三角形的边长为:"+l);
}
}
}
3.8
import java.util.Scanner;
public class Demo3_8 {
public static void main(String[] args) {
//1.用户输入年、月、该月的哪天
Scanner scanner=new Scanner(System.in);
System.out.print("Enter year:(e.g.,2012):");
int year=scanner.nextInt();
System.out.print("Enter month:");
int month=scanner.nextInt();
System.out.print("Enter the day of the month:");
int q=scanner.nextInt();
int m=month%12;
switch (m) {
case 1:
m=13;
year-=1;
break;
case 2:
m=14;
year-=1;
break;
default:
break;
}
int j=year/100;
int k=year%100;
//2.计算h
int h=(q+26*(m+1)/10+k+k/4+j/4+5*j)%7;
//3.switch循环判定是周几
switch (h) {
case 0:
System.out.println("Day of the week is Saturday");
break;
case 1:
System.out.println("Day of the week is Sunday");
break;
case 2:
System.out.println("Day of the week is Monday");
break;
case 3:
System.out.println("Day of the week is Tuesday");
break;
case 4:
System.out.println("Day of the week is Wednesday");
break;
case 5:
System.out.println("Day of the week is Thursday");
break;
case 6:
System.out.println("Day of the week is Friday");
break;
}
}
}
import java.util.Scanner;
public class Demo3_9 {
public static void main(String[] args) {
//1.输入一个点
Scanner scanner=new Scanner(System.in);
System.out.print("Enter a point with two coordinates:");
double x1=scanner.nextDouble();
double y1=scanner.nextDouble();
//2.计算点到圆心的距离
double distance=Math.sqrt(Math.pow(x1, 2)+Math.pow(y1, 2));
//3.判断点是否在圆内
if(distance<=10){
System.out.println ("Point("+x1+","+y1+") is in the circle");
}else{
System.out.println("Point ("+x1+","+y1+") is not in the circle");
}
}
}
import java.util.Scanner;
public class Demo3_10 {
public static void main(String[] args) {
//1.输入点的坐标
Scanner scanner=new Scanner(System.in);
System.out.print("Enter a point with two coordinates:");
double x1=scanner.nextDouble();
double y1=scanner.nextDouble();
//2.判断点是否在矩形内
if(x1<=10/2&&y1<=5.0/2){
System.out.println ("Point("+x1+","+y1+") is in the rectangle");
}else{
System.out.println ("Point("+x1+","+y1+") is not in the rectangle");
}
}
}
import java.util.Scanner;
public class Demo3_11 {
public static void main(String[] args) {
Random random = new Random();
int num = random.nextInt(13);
String a = "";
switch(num){
case 0:
a = "Ace";
break;
case 1:
a = "2";
break;
case 2:
a = "3";
break;
case 3:
a = "4";
break;
case 4:
a = "5";
break;
case 5:
a = "6";
break;
case 6:
a = "7";
break;
case 7:
a = "8";
break;
case 8:
a = "9";
break;
case 9:
a = "10";
break;
case 10:
a = "Jack";
break;
case 11:
a = "Queen";
break;
case 12:
a = "King";
break;
}
int number = (int)(Math.random()*4);
String b = "";
switch(number%4){
case 0:
b = "Clubs";
break;
case 1:
b = "Diamonds";
break;
case 2:
b = "Hearts";
break;
case 3:
b = "Spades";
break;
}
System.out.println("The card you picked is "+a+" of "+b);
}
}
import java.util.Scanner;
public class Demo3_12 {
public static void main(String[] args) {
//1.输入第一条直线上的点和第二条直线上的点
Scanner scanner=new Scanner(System.in);
System.out.print("Enter x1,y1,x2,y2,x3,y3,x4,y4");
double x1=scanner.nextDouble();
double y1=scanner.nextDouble();
double x2=scanner.nextDouble();
double y2=scanner.nextDouble();
double x3=scanner.nextDouble();
double y3=scanner.nextDouble();
double x4=scanner.nextDouble();
double y4=scanner.nextDouble();
//2.结合方程组计算方程组中的系数和常数项
double a=y1-y2;
double b=-(x1-x2);
double c=y3-y4;
double d=-(x3-x4);
double e=a*x1+b*y1;
double f=c*x3+d*y3;
//3.判断方程组是否有解
double delt=a*d-b*c;
if(delt==0){
System.out.print("两线平行");
}else{
double x=(e*d-b*f)/(a*d-b*c);
double y=(a*f-e*c)/(a*d-b*c);
System.out.println("x is "+x+" and y is "+y);
}
}
}
3.13
import java.util.Scanner;
public class Demo3_13 {
public static void main(String[] args) {
//1.输入点的坐标
Scanner scanner=new Scanner(System.in);
System.out.print("输入点的坐标:");
double x=scanner.nextDouble();
double y=scanner.nextDouble();
//2.判断点在三角形内
// if(x>=0&&y>=0&&x<=(y-100)/-0.5&&(y<=-0.5*x+100)){
// System.out.print("in");
// }else{
// System.out.print("out");
// }
if(x>=0&&x<=200){
if((200-x)/y>=2){
System.out.println("in");
return;//直接结束函数
}
}
System.out.println("out");
}
}
import java.util.Scanner;
public class Demo3_14 {
public static void main(String[] args) {
//1.输入中心坐标以及宽,高
Scanner scanner=new Scanner(System.in);
System.out.print("Enter r1's center x-,y-coordinates,width,and height:");
double rx1=scanner.nextDouble();
double ry1=scanner.nextDouble();
double w1=scanner.nextDouble();
double h1=scanner.nextDouble();
System.out.print("Enter r2's center x-,y-coordinates,width,and height:");
double rx2=scanner.nextDouble();
double ry2=scanner.nextDouble();
double w2=scanner.nextDouble();
double h2=scanner.nextDouble();
//2.计算是否r2在r1内
if(rx2<=(w1/2-w2/2+rx1)&&rx2>=(rx1-w1/2+w2/2)&&ry2<=(h1/2-h2/2+ry1)&&ry2>=(ry1-h2/2-h1/2)){
System.out.println("r2 is inside r1");
}else if(rx2>=(w1/2+w2/2+rx1)||rx2<=(rx1-w1/2-w2/2)||ry2>=(h1/2+h2/2+ry1)||ry2<=(ry1-h2/2-h1/2)){
System.out.println("r2 does not overlap r1");
}else{
System.out.println("r2 overlaps r1");
}
}
}
3.15
import java.util.Scanner;
public class Demo3_15 {
public static void main(String[] args) {
//1.输入两圆的中心坐标和各自半径的值
Scanner scanner=new Scanner(System.in);
System.out.print("Enter circle1's center x-,y-coordinates,and radius:");
double x1=scanner.nextDouble();
double y1=scanner.nextDouble();
double r1=scanner.nextDouble();
System.out.print("Enter circle2's center x-,y-coordinates,and radius:");
double x2=scanner.nextDouble();
double y2=scanner.nextDouble();
double r2=scanner.nextDouble();
//2.计算圆心距离
double distance=Math.sqrt(Math.pow(x1-x2, 2)+Math.pow(y1-y2,2));
//3.判断圆的位置
if(distance<=r1-r2){
System.out.println("circle2 is inside circle1");
}else if(distance>=r1+r2){
System.out.println("circle2 does not overlap circle1");
}else{
System.out.println("circle2 overlaps circle1");
}
}
}
import java.util.Scanner;
public class Demo3_16 {
public static void main(String[] args) {
//1.输入p0,p1,p2的坐标
Scanner scanner=new Scanner(System.in);
System.out.print("Enter three points for p0,p1 and p2:");
double x0=scanner.nextDouble();
double y0=scanner.nextDouble();
double x1=scanner.nextDouble();
double y1=scanner.nextDouble();
double x2=scanner.nextDouble();
double y2=scanner.nextDouble();
//2.计算
double number=(x1-x0)*(y2-y0)-(x2-x0)*(y1-y0);
//3.判断
if(number>0){
System.out.println("("+x2+","+y2+")is on the left side of the line from ("+x0+","+y0+") to ("+x1+","+y1+")");
}else if(number<0){
System.out.println("("+x2+","+y2+")is on the right side of the line from ("+x0+","+y0+") to ("+x1+","+y1+")");
}else{
System.out.println("("+x2+","+y2+")is on the line from ("+x0+","+y0+") to ("+x1+","+y1+")");
}
}
}