// Bad
if (variable.equals("literal")) { ... }
// Good
if ("literal".equals(variable)) { ... }

String[] files = file.list();
// Watch out
if (files != null) {
 for (int i = 0; i < files.length; i++) {
 ...
 }
}

if (file.isDirectory()) {
 String[] files = file.list();
 // Watch out
 if (files != null) {
 for (int i = 0; i < files.length; i++) {
  ...
 }
 }
}

// Bad
if (string.indexOf(character) != -1) { ... }
// Good
if (string.indexOf(character) >= 0) { ... }

// Ooops
if (variable = 5) { ... }
// Better (because causes an error)
if (5 = variable) { ... }
// Intent (remember. Paranoid JavaScript: ===)
if (5 === variable) { ... }

// Bad
if (array.length > 0) { ... }
// Good
if (array != null && array.length > 0) { ... }

// Bad
public void boom() { ... }
// Good. Don't touch.
public final void dontTouch() { ... }

// Bad
void input(String importantMessage) {
 String answer = "...";
 answer = importantMessage = "LOL accident";
}
// Good
final void input(final String importantMessage) {
 final String answer = "...";
}

// Bad
<T> void bad(T value) {
 bad(Collections.singletonList(value));
}
<T> void bad(List<T> values) {
 ...
}
// Good
final <T> void good(final T value) {
 if (value instanceof List)
 good((List<?>) value);
 else
 good(Collections.singletonList(value));
}
final <T> void good(final List<T> values) {
 ...
}

// This library sucks
@SuppressWarnings("all")
Object t = (Object) (List) Arrays.asList("abc");
bad(t);

// Bad
switch (value) {
 case 1: foo(); break;
 case 2: bar(); break;
}
// Good
switch (value) {
 case 1: foo(); break;
 case 2: bar(); break;
 default:
 throw new ThreadDeath("That'll teach them");
}

// Bad, doesn't compile
switch (value) {
 case 1: int j = 1; break;
 case 2: int j = 2; break;
}
// Good
switch (value) {
 case 1: {
 final int j = 1;
 break;
 }
 case 2: {
 final int j = 2;
 break;
 }
 // Remember:
 default: 
 throw new ThreadDeath("That'll teach them");
}