Default values in java

Question

Hi I am having the following code. when i am using instance variables i am getting the output as follows(Default Values)

int value: 0
float value: 0.0
String value: null
Static int value: 0

But if i try declare the local variable and print the default value it is giving an error that the variable should be initialized. Can any one explain me the reason please?

public class DefaultValues {
  int a;
  float b;
  String c;
  static int d;
  public static void main(String[] args) {      
    int e;                                     // <----
    DefaultValues dv = new DefaultValues();
    System.out.println("int value: "+dv.a);
    System.out.println("float value: "+dv.b);
    System.out.println("String value: "+dv.c);
    System.out.println("Static int value: "+d);
    System.out.println("local int value: "+e); // <----
  }
}

Local variables do not have a default value. They must be initialized before they are used. — Sotirios Delimanolis, Jan 06 '14 at 05:28

score 2 · Accepted Answer · edited Jan 06 '14 at 05:43

2

Only instance variables, static(Class) variables and array components are initialized to default values.

Local variables cannot be used unless they are initialized as they are not assigned default values.

edited Jan 06 '14 at 05:43

vanza

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answered Jan 06 '14 at 05:32

Aniket Thakur

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2

_are arrays_ Did you mean to say something else? – Sotirios Delimanolis Jan 06 '14 at 05:37
Yes **An array initializer creates an array and provides initial values for all its components** as per JLS. – Aniket Thakur Jan 06 '14 at 05:40
Oh got your point now. Thanks! – Aniket Thakur Jan 06 '14 at 05:42

score 1 · Answer 2 · answered Jan 06 '14 at 05:38

From Java Language Specification 3.0, 4.12.5 Initial Values of Variables:

A local variable (§14.4, §14.14) must be explicitly given a value before it is used, by either initialization (§14.4) or assignment (§15.26), in a way that can be verified by the compiler using the rules for definite assignment (§16).

score 1 · Answer 3 · edited Jan 06 '14 at 05:44

We may have uninitialied local vars but compiler will not allow to use unless we explicitly intialize them. This is Java language rule. See JLS 4.12.5. Initial Values of Variables http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html

•A local variable (§14.4, §14.14) must be explicitly given a value before it is used, by either initialization (§14.4) or assignment (§15.26), in a way that can be verified using the rules for definite assignment (§16).

score 1 · Answer 4 · edited Jan 06 '14 at 05:50

For Class members(variable) JVM will put the default values or initialize it by default value, for a local variables it makes you assign and initial value before accessing the variable.

From Doc :

It's not always necessary to assign a value when a field is declared. Fields that are declared but not initialized will be set to a reasonable default by the compiler. Generally speaking, this default will be zero or null, depending on the data type. Relying on such default values, however, is generally considered bad programming style.

You can check the Default Values of different datatype in Primitive Data Types for more information about the class members default values.

Default values in java

4 Answers4