Control flow textbook series (a) - Java's conditional statements If
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conditional
Step 1: if
Step 2: Multi-expression with an expression
Step 3: if the course may encounter pits
step 4: if else
step 5: else if
step 6: practice -BMI
step 7: The answer -BMI
Example 1: if
if(表达式1){
表达式2；
}
If the value of the expression 1 is true,
on the implementation of the expression 2
if
public class HelloWorld {
public static void main(String[] args) {
boolean b = true;
//如果成立就打印yes
if(b){
System.out.println("yes");
}
}
}
Example 2: Multi-expression and expression
public class HelloWorld {
public static void main(String[] args) {
boolean b = false;
//如果有多个表达式，必须用大括弧包括起来
if(b){
System.out.println("yes1");
System.out.println("yes2");
System.out.println("yes3");
}
//否则表达式2 3 无论b是否为true都会执行
if(b)
System.out.println("yes1");
System.out.println("yes2");
System.out.println("yes3");
//如果只有一个表达式可以不用写括弧，看上去会简约一些
if(b){
System.out.println("yes1");
}
if(b)
System.out.println("yes1");
}
}
Example 3: pit if the course may be encountered
in the back row 6, if there is a semicolon; semicolon is a complete expression
if b is true, this will be the implementation of a semicolon, then print yes
if b is false, does not perform the semicolon, and then print yes
, seem anyway yes Print
public class HelloWorld {
public static void main(String[] args) {
boolean b = false;
if (b);
System.out.println("yes");
}
}
Example 4: if else
case on behalf else does not hold
if else
public class HelloWorld {
public static void main(String[] args) {
boolean b = false;
if (b)
System.out.println("yes");
else
System.out.println("no");
}
}
Example. 5: IF the else
the else condition is determined is a multi-IF
public class HelloWorld {
public static void main(String[] args) {
//如果只使用 if,会执行4次判断
int i = 2;
if (i==1)
System.out.println(1);
if (i==2)
System.out.println(2);
if (i==3)
System.out.println(3);
if (i==4)
System.out.println(4);
//如果使用else if, 一旦在18行，判断成立， 20行和22行的判断就不会执行了，节约了运算资源
if (i==1)
System.out.println(1);
else if (i==2)
System.out.println(2);
else if (i==3)
System.out.println(3);
else if (i==4)
System.out.println(4);
}
}
