4.6 How to handle multiple branches correctly?

A. Introduction:

Sometimes, nested if statements may have many layers. For example, if you want to write a program to display the effect of an earthquake, as measured by the Richter scale below.

You will need 4 nested if statements

The code may look like:

if (richter >= 8.0) {
  description = "Most structures fall";
} else if (richter >= 7.0) {  description = "Many buildings destroyed";
} else if (richter >= 6.0) {  description = "Many buildings considerably damaged, some collapse"; 
} else if (richter >= 4.5) {  description = "Damage to poorly constructed buildings"; 
} else {  description = "No destruction of buildings"; }

(1). Notice if you reverse the order of if statements, the results will be wrong.

if (richter >= 4.5) // Tests in wrong order {
  description = "Damage to poorly constructed buildings"; 
  } else if (richter >= 6.0) {  description = "Many buildings considerably damaged, some collapse"; 
  } else if (richter >= 7.0) {  description = "Many buildings destroyed"; 
  } else if (richter >= 8.0) {  description = "Most structures fall"; }

(2). Skipping the "else" statements will also be wrong:

// Didn’t use else 
if (richter >= 8.0) {  description = "Most structures fall"; } 
if (richter >= 7.0) {  description = "Many buildings destroyed"; } 
if (richter >= 6.0) {  description = "Many buildings considerably damaged, some collapse"; } 
if (richter >= 4.5) {  "Damage to poorly constructed buildings"; }

(3). Sometimes, to keep clarity, we use a "switch" statement instead of a nested if statements. For example, to convert an Arabic digit to a Roman numeral:

String digitR = "";
int digit = ...; 
if (digit == 1) { digitR = "I"; } 
else if (digit == 2) { digitR = "II"; } 
else if (digit == 3) { digitR = "III"; } 
else if (digit == 4) { digitR = "IV"; } 
else if (digit == 5) { digitR = "V"; } 
else if (digit == 6) { digitR = "VI"; } 
else if (digit == 7) { digitR = "VII"; } 
else if (digit == 8) { digitR = "VIII"; } 
else if (digit == 9) { digitR = "IX"; } 
else { System.out.println("The Arabic digit is wrong!"); } 

You can also use:

String digitR = "";
int digit = . . .; 
switch (digit) {  // the variable can be of type int, char or String
case 1: digitR = "I"; break;  // case 1 will be case '1' or case "1" if the switch variable is char or String
case 2: digitR = "II"; break;  
case 3: digitR = "III"; break;  
case 4: digitR = "IV"; break;  
case 5: digitR = "V"; break;  
case 6: digitR = "VI"; break;  
case 7: digitR = "VII"; break;  
case 8: digitR = "VII"; break;  
case 9: digitR = "IX"; break;  
default: System.out.println("The Arabic digit is wrong!"); }