If you have a method into which you pass a String parameter that you compare with another string then:

 void foo( String str ){  String CONST_STR = "bar";  // DON'T COMPARE LIKE THIS:  //if ( str == CONST_STR ) )  // AND DON'T COMPARE LIKE THIS  // if ( str.equals( CONST_STR ) )  // JUST COMPARE LIKE THIS:  if ( CONST_STR.equals( str ) )  {}  // OR LIKE THIS:  if ( "bar".equals( str ) )  {}}

This way you don’t have to protect yourself against a null being passed into the method.