grammar structure:
if(布尔表达式){
//语句块1
}else{
// 语句块2
}
When the Boolean expression is true, execute statement block 1, otherwise, the statement block 2. That is, the else. Flow chart shown in Figure 3-3.
3-3 if-else double-selection structure flowchart of FIG.
[Example 3-2] if-else structure
public class Test2 {
public static void main(String[] args) {
//随机产生一个[0.0, 4.0)区间的半径，并根据半径求圆的面积和周长
double r = 4 * Math.random();
//Math.pow(r, 2)求半径r的平方
double area = Math.PI * Math.pow(r, 2);
double circle = 2 * Math.PI * r;
System.out.println("半径为： " + r);
System.out.println("面积为： " + area);
System.out.println("周长为： " + circle);
//如果面积>=周长，则输出"面积大于等于周长"，否则，输出周长大于面积
if(area >= circle) {
System.out.println("面积大于等于周长");
} else {
System.out.println("周长大于面积");
}
}
}running result:
FIG 3-4 FIG running effect Example 3-2
public class Test3 {
public static void main(String[] args) {
int a=2;
int b=3;
if (a<b) {
System.out.println(a);
} else {
System.out.println(b);
}
}
}The conditional operator may sometimes be used instead if-else, as shown in Example 3-3 and Example 3-4.
[Example 3-3] using if-else
FIG 3-5 FIG running effect Example 3-3
[Example 3-4] using the conditional operator
public class Test4 {
public static void main(String[] args) {
int a=2;
int b=3;
System.out.println((a<b)?a:b);
}
}
Example 3-4 3-6 run renderings
