Java SE 7 Features

New Java SE 7 programming language features

• Binary Literals: The integral types (byte, short, int, and long) can also be expressed using the binary number system. To specify a binary literal, add the prefix 0b or 0B to the number.
• Strings in switch Statements: You can use a String object in the expression of a switch statement
• The try-with-resources Statement: The try-with-resources statement is a try statement that declares one or more resources. A resource is as an object that must be closed after the program is finished with it. The try-with-resources statement ensures that each resource is closed at the end of the statement. Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.
• Catching Multiple Exception Types and Rethrowing Exceptions with Improved Type Checking: a single catch block can handle more than one type of exception. This feature can reduce code duplication and lessen the temptation to catch an overly broad exception.
• Underscores in Numeric Literals: Any number of underscore characters (_) can appear anywhere between digits in a numerical literal. This feature enables you, for example, to separate groups of digits in numeric literals, which can improve the readability of your code.
• Type Inference for Generic Instance Creation: You can replace the type arguments required to invoke the constructor of a generic class with an empty set of type parameters (<>) as long as the compiler can infer the type arguments from the context. This pair of angle brackets is informally called the diamond.
• Improved Compiler Warnings and Errors When Using Non-Reifiable Formal Parameters with Varargs Methods

Binary Literals

// An 8-bit 'byte' value:
byte aByte = (byte)0b00100001;

// A 16-bit 'short' value:
short aShort = (short)0b1010000101000101;

// Some 32-bit 'int' values:
int anInt1 = 0b10100001010001011010000101000101;
int anInt2 = 0b101;
int anInt3 = 0B101; // The B can be upper or lower case.

// A 64-bit 'long' value. Note the "L" suffix:
long aLong = 0b1010000101000101101000010100010110100001010001011010000101000101L;

The try-with-resources statement

The example reads the first line from a file. It uses an instance of BufferedReader to read data from the file. BufferedReader is a resource that must be closed after the program is finished with it:

static String readFirstLineFromFile(String path) throws IOException {
  try (BufferedReader br = new BufferedReader(new FileReader(path))) {
    return br.readLine();
  }
}

In this example, the resource declared in the try-with-resources statement is a BufferedReader. The declaration statement appears within parentheses immediately after the try keyword. The class BufferedReader, in Java SE 7 and later, implements the interface java.lang.AutoCloseable. Because the BufferedReader instance is declared in a try-with-resource statement, it will be closed regardless of whether the try statement completes normally or abruptly (as a result of the method BufferedReader.readLine throwing an IOException).

Underscores in Numeric Literals

The following example shows other ways you can use the underscore in numeric literals:

long creditCardNumber = 1234_5678_9012_3456L;
long socialSecurityNumber = 999_99_9999L;
float pi = 3.14_15F;
long hexBytes = 0xFF_EC_DE_5E;
long hexWords = 0xCAFE_BABE;
long maxLong = 0x7fff_ffff_ffff_ffffL;
byte nybbles = 0b0010_0101;
long bytes = 0b11010010_01101001_10010100_10010010;

You can place underscores only between digits; you cannot place underscores in the following places:

• At the beginning or end of a number
• Adjacent to a decimal point in a floating point literal
• Prior to an F or L suffix
• In positions where a string of digits is expected

Type Inference for Generic Instance Creation

You can use

Map<String, List<String>> myMap = new HashMap<>();

instead of

Map<String, List<String>> myMap = new HashMap<String, List<String>>();

However, you can’t use

List<String> list = new ArrayList<>();
list.add("A");

  // The following statement should fail since addAll expects
  // Collection<? extends String>

list.addAll(new ArrayList<>());

because it can’t compile. Note that the diamond often works in method calls; however, it is suggested that you use the diamond primarily for variable declarations.

Strings in switch Statements

public String getTypeOfDayWithSwitchStatement(String dayOfWeekArg) {
     String typeOfDay;
     switch (dayOfWeekArg) {
         case "Monday":
             typeOfDay = "Start of work week";
             break;
         case "Tuesday":
         case "Wednesday":
         case "Thursday":
             typeOfDay = "Midweek";
             break;
         case "Friday":
             typeOfDay = "End of work week";
             break;
         case "Saturday":
         case "Sunday":
             typeOfDay = "Weekend";
             break;
         default:
             throw new IllegalArgumentException("Invalid day of the week: " + dayOfWeekArg);
     }
     return typeOfDay;
}

Remarks

Enhancements in Java SE 7