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The Java Lesson 7

Bitwise operations: overview with detailed examples

1. Logical bitwise operations
2. The complement operator
3. Bitwise shift operations
4. Bitwise assignment operations andr review questions

Bitwise assignment operations

• All bitwise operators except the unary complement (~) can be combined with assignment as long as the first operand is an integer variable. For example,

int x = 23;
x <<= 2;
System.out.println("Now x is " + x);

will display "Now x is 92" because 0000 0017 shifted 2 bits to the left becomes 0000 005C.

• Do not require casts to prevent compile errors. Possible data loss is ignored (so be careful). For example,

byte x = 127;
x |= 256;
System.out.println("Now x is " + x);

will display "Now x is 127" because 7F OR 0000 0100 results in 0000 017F (decimal 383) but only the right-most 8 bits are assigned to byte variable x.

More practice

The Java ranch tutorial Cat and Mouse Games with Bits ends with an applet you can use to practice bitwise operations.

Review questions

1. If x is short variable with a decimal value of 27, what data type and decimal value will result from executing the following expression?

x & 8

1. a short with a value of 8

2. an int with a value of 8

3. a short with a value of 27

4. an int with a value of 27

5. a short with a value of 19

2. If someNumber is an int variable having some value, what value will it have after executing the following statement?

someNumber ^= someNumber;

1. the statement will not compile

2. the statement will compile but an error will occur at run time

3. 0

4. -1

5. the value cannot be determined from the information given

3. If amount is a short variable with a decimal value of 6, which of the following statements will multiply amount by four and store the result in a short variable named newAmount? (choose two)

1. newAmount = (short) (amount << 2);

2. newAmount = amount << 2;

3. newAmount = (short) (amount >> 2);

4. newAmount = amount >> 2;

5. newAmount = (short) (amount << 34);

4. If x is an int variable with an initial value of 7, what value will it have after executing the following?

x >>>= (x ^ 6);

1. 0

2. 3

3. 14

4. 448

5. the statement will not compile

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