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# 【Java】制御構文ノート

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# 制御構文

## 構造化定理

• 順次
• 分岐
• `if`, `switch`
• 繰り返し
• `while`,`for`

## 分岐

• `if`
• `switch`
```// if構文
int r=new java.util.Random().nextInt(2);
if (r<1){
System.out.println("This is true by 'if'.");
}else{
System.out.println("This is false by 'if'.");
}

// switch構文
int s=new java.util.Random().nextInt(3);
switch(s){
case 0:
System.out.println("This is Case.0 by 'switch'.");
break;
case 1:
System.out.println("This is Case.1 by 'switch'.");
break;
case 2:
System.out.println("This is Case.2 by 'switch'.");
break;
default:
System.out.println("This is default by 'switch'.");
}
```

## 繰り返し

• `while`
• `do while`
• `for`
```// while構文
int w=1;
while(w<4){
System.out.println("Count No."+w+" by 'while'.");
w++;
}

// do while構文
int dw=3;
do{
System.out.println("Count No."+dw+" by 'do while'.");
dw--;
System.out.println("Count decrease -1 by 'do while'.");
}while(dw>0);

// for構文
for(int i=1; i<=3; i++){
System.out.println("Count No."+i+" by 'for'.");
}

```

## 「繰り返しの中断」という概念

• `continue`：ループを続ける。
• `break`：ループを抜ける。
```// 繰り返しの中断
for(int i=5; i>=1; i--){
if(i==3){
continue;
}
if(i==2){
break;
}
System.out.println("Count No."+i+" by 'for/continue(3)/break(2)'.");
}
```

# 参考書籍

スッキリわかるJava入門第２版
Pp.098-133.

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