Java branch structure - if /en. else / switch
Sequence structure only the order of execution can not be judgments and choices, and therefore require a branched structure.
Java has two branch structure:
- if statement
- switch statement
if statement
If a statement contains a boolean expression and one or more statements.
grammar
If the statement with the following syntax:
if(布尔表达式) { //如果布尔表达式为true将执行的语句 }
If the Boolean expression evaluates to true, the if statement block of code. Otherwise If statement block behind the code execution.
public class Test { public static void main(String args[]){ int x = 10; if( x < 20 ){ System.out.print("这是 if 语句"); } } }
The above code is compiled results are as follows:
这是 if 语句
if /en. else statement
Later if statement with else statements when the boolean expression of the if statement is false, else statement block is executed.
grammar
if /en. else used as follows:
if(布尔表达式){ //如果布尔表达式的值为true }else{ //如果布尔表达式的值为false }
Examples
public class Test { public static void main(String args[]){ int x = 30; if( x < 20 ){ System.out.print("这是 if 语句"); }else{ System.out.print("这是 else 语句"); } } }
The above code is compiled results are as follows:
这是 else 语句
if /en. else if /en. else statement
Later if statement with elseif /en. else statement, this statement can detect a variety of possible scenarios.
Use if, else if, else statement, the need for attention to the following points:
- if the statement at most one else statements before all else statements elseif statements.
- If statements can have several elseif statements, they must be before the else statement.
- Once one else if statement is detected as true, other else if and else statements are skipped executed.
grammar
if /en. else syntax is as follows:
if(布尔表达式 1){ //如果布尔表达式 1的值为true执行代码 }else if(布尔表达式 2){ //如果布尔表达式 2的值为true执行代码 }else if(布尔表达式 3){ //如果布尔表达式 3的值为true执行代码 }else { //如果以上布尔表达式都不为true执行代码 }
Examples
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"); } } }
The above code is compiled results are as follows:
Value of X is 30
Nested if /en. else statement
Nested if-else statement is legitimate. This means that you can use if or elseif statement in another if or elseif statement.
grammar
Nested if /en. else syntax is as follows:
if(布尔表达式 1){ ////如果布尔表达式 1的值为true执行代码 if(布尔表达式 2){ ////如果布尔表达式 2的值为true执行代码 } }
You can be like the if statement nested else if /en. else.
Examples
public class Test { public static void main(String args[]){ int x = 30; int y = 10; if( x == 30 ){ if( y == 10 ){ System.out.print("X = 30 and Y = 10"); } } } }
The above code is compiled results are as follows:
X = 30 and Y = 10
switch statement
switch statement to determine a value of a variable with a range of values are equal, and each value is called a branch.
grammar
switch syntax is as follows:
switch(expression){ case value : //语句 break; //可选 case value : //语句 break; //可选 //你可以有任意数量的case语句 default : //可选 //语句 }
switch statement has the following rules:
- switch statement only variable type is byte, short, int or char.
- switch statement can have multiple case statements. Behind each case followed by a colon and the value to be compared.
- case statement data type of value must be the same as the data type of the variable, and can only be a constant or literal.
- When the value of a variable equal to the value of case statement, the statement after the case statement is executed until the break statement would appear out of the switch statement. 3
- When it encounters a break statement, switch statement is terminated. The program jumps to the statement following the switch statement is executed. case statement does not have to contain a break statement. If there is no break statement appears, the program will continue with the next case statement until the break statement.
- switch statement can contain a default branch that must be the last branch of the switch statement. default execution in no case statements and variable values equal time. default branch do not need to break the statement.
Examples
public class Test { public static void main(String args[]){ //char grade = args[0].charAt(0); char grade = 'C'; switch(grade) { case 'A' : System.out.println("Excellent!"); break; case 'B' : case 'C' : System.out.println("Well done"); break; case 'D' : System.out.println("You passed"); case 'F' : System.out.println("Better try again"); break; default : System.out.println("Invalid grade"); } System.out.println("Your grade is " + grade); } }
The above code is compiled results are as follows:
Well done Your grade is C