11.Javaシーケンス構造と選択構造(ifとswitch)
知識点:
シーケンス構造:
単一選択if:
二重選択if else:
複数選択if...if else...else:
ifネスト:
switch...caseマルチ選択:
/*Java : , , ,
1. : 。
2. :
if( ) :
if( ){
true
}
if...else( ) :
if( ){
true
}else{
false
}
if...else if...else( ) :
if( 1){
1 true
}else if( 2){
2 true
}else if( 3){
3 true
}else{
true
}
if :
if, if...else, if...else if...else
: if
if else
if if else else
switch...case( ):
:switch( ){
case 1:
break;
case 2:
break;
default:
}
:break:( break )。default:(case break )
break default ,
switch :
! byte,short,int,char;
boolean ;long,float double int, int , int 。
! String;
switch , String 。
*/
シーケンス構造:
public class D1 {
public static void main(String[] args) {
System.out.println(1);
System.out.println(2);
System.out.println(3);
}
}
単一選択if:
public class D2 {
public static void main(String[] args) {
Scanner sca=new Scanner(System.in);
System.out.println(" ");
String str=sca.nextLine();
//equals:
if (str.equals("Hello")==true){
System.out.println(str);// Hello ,
}
System.out.println("End");//
sca.close();
}
}
二重選択if else:
public class D3 {
public static void main(String[] args) {
// 18 ,
Scanner sca=new Scanner(System.in);
System.out.println(" ");
double age=sca.nextDouble();
if (age>=18){
System.out.println(" ");
}else{
System.out.println(" ");
}
sca.close();
}
}
複数選択if...if else...else:
public class D4 {
public static void main(String[] args) {
// 90 100 A,80 89 B,70 79 C,60 69 D,0 59 E,
Scanner sca=new Scanner(System.in);
System.out.println(" :");
double score=sca.nextDouble();
if(score>89&&score<=100==true){
System.out.println(" A");
}else if(score>79&&score<90){
System.out.println(" B");
}else if(score>69&&score<80){
System.out.println(" C");
}else if(score>59&&score<70){
System.out.println(" D");
}else if(score>=0&&score<60){
System.out.println(" E");
}else{
System.out.println(" ");
}
sca.close();
}
}
ifネスト:
public class D5 {
public static void main(String[] args) {
// 0-10 :
int num=(int)(Math.random()*10);
// 0-10 :
if (num<=10&&num>5){
if (num==9){
System.out.println(num);
}else if (num==8){
System.out.println(num);
}else if (num==7){
System.out.println(num);
}else{
System.out.println(num);
}
}else if(num>0&&num<6){
if (num==5){
System.out.println(num);
}else if(num==4){
System.out.println(num);
}else if(num==3){
System.out.println(num);
}else if(num==2){
System.out.println(num);
}else{
System.out.println(num);
}
}else{
System.out.println(num);
}
}
}
switch...caseマルチ選択:
public class D7_switch {
public static void main(String[] args) {
String name=" ";
switch (name){
case " ":
break;
case " ":
break;
default:
System.out.println(" ");
}
}
}