If in Java controls the branch structure, it means that if the condition is true, a certain piece of code will be executed.
if statement
An if statement contains a Boolean expression and one or more statements.
Grammar
The syntax of the If statement is as follows:
if(布爾表達式)
{
//如果布爾表達式為true將執(zhí)行的語句
}If the value of the Boolean expression is true, the code block in the if statement is executed. . Otherwise, the code following the If statement block is executed.
public class Test {
public static void main(String args[]){
int x = 10;
if( x < 20 ){
System.out.print("這是 if 語句");
}
}
}The compilation and running results of the above code are as follows:
這是 if 語句
if...else statement
The if statement can be followed by an else statement. When the if statement When the Boolean expression value is false, the else statement block will be executed.
Grammar
if...else is used as follows:
if(布爾表達式){
//如果布爾表達式的值為true
}else{
//如果布爾表達式的值為false
}Example
public class Test {
public static void main(String args[]){
int x = 30;
if( x < 20 ){
System.out.print("這是 if 語句");
}else{
System.out.print("這是 else 語句");
}
}
}The above code is compiled The running results are as follows:
這是 else 語句
if...else if...else statement
The if statement can be followed by elseif...else statement, which can be detected Many possible scenarios.
When using if, else if, else statements, you need to pay attention to the following points:
(1) The if statement has at most one else statement, and the else statement comes after all elseif statements.
(2) The If statement can have several elseif statements, and they must precede the else statement.
(3) Once one of the else if statements is detected as true, the execution of the other else if and else statements will be skipped.
Grammar
if...else syntax format is as follows:
if(布爾表達式 1){
//如果布爾表達式 1的值為true執(zhí)行代碼
}else if(布爾表達式 2){
//如果布爾表達式 2的值為true執(zhí)行代碼
}else if(布爾表達式 3){
//如果布爾表達式 3的值為true執(zhí)行代碼
}else {
//如果以上布爾表達式都不為true執(zhí)行代碼
}Example
public class Test {
public static void main(String args[]){
int x = 30;
if( x == 10 ){
System.out.print("Value of X is 10");
}else if( x == 20 ){
System.out.print("Value of X is 20");
}else if( x == 30 ){
System.out.print("Value of X is 30");
}else{
System.out.print("This is else statement");
}
}
}above The code compilation and running results are as follows:
Value of X is 30
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