OCA Java SE 8 Method - Java Method Declaration

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For example, we can write a basic method.

public final void myMethod(int minutes) throws InterruptedException { 
    // method body
} 

This is called a method declaration, which specifies all the information needed to call the method.

To call this method, just type its name, followed by a single int value in parentheses:

myMethod(10); 

Access Modifiers

Java offers four choices of access modifier:

Modifier	Meaning
public	The method can be called from any class.
private	The method can only be called from within the same class.
protected	The method can only be called from classes in the same package or subclasses.
Default (Package Private) Access	The method can only be called from classes in the same package. There is no keyword for default access. Just omit the access modifier.

myMethod1() is a valid method declaration with public access.

public void myMethod1() {} 

myMethod2() doesn't compile because default is not a valid access modifier.

default void myMethod2() {} // DOES NOT COMPILE 

myMethod3() doesn't compile because the access modifier is specified after the return type.

void public myMethod3() {} // DOES NOT COMPILE 

myMethod4() is a valid method declaration with default access.

void myMethod4() {} 

Optional Specifiers

There are a number of optional specifiers in the following list.

Unlike with access modifiers, you can have multiple specifiers in the same method although not all combinations are legal.

When this happens, you can specify them in any order.

You can have zero or more specifiers in a method declaration.

Specifiers	Meaning
static	Used for class methods.
abstract	Used when not providing a method body.
final	Used when a method is not allowed to be overridden by a subclass.
synchronized	On the OCP but not the OCA exam.
native	Not on the OCA or OCP exam. Used with code written in another language such as C++.
strictfp	Not on the OCA or OCP exam. Used for making floating-point calculations portable.

myMethod1() is a valid method declaration with no optional specifier.

public void myMethod1() {} 

myMethod2() is a valid method declaration, with final as the optional specifier.

public final void myMethod2() {} 

myMethod3() and myMethod4() are valid method declarations with both final and static as optional specifiers. The order of these two keywords doesn't matter.

public static final void myMethod3() {}  
public final static void myMethod4() {} 

myMethod5() doesn't compile because modifier is not a valid optional specifier.

public modifier void myMethod5() {} // DOES NOT COMPILE 

myMethod6() doesn't compile because the optional specifier is after the return type.

public void final myMethod6() {} // DOES NOT COMPILE 

myMethod7() does compile. Java allows the optional specifiers to appear before the access modifier.

final public void myMethod7() {} 

Return Type

The return type might be an actual Java type such as String or int.

If there is no return type, the void keyword is used.

void means without contents.

Remember that a method must have a return type. If no value is returned, the return type is void. You cannot omit the return type.

Methods with a return type other than void MUST have a return statement inside the method body.

This return statement must include the primitive or object to be returned.

Methods that have a return type of void can have a return statement with no value returned or omit the return statement entirely.

Since the return type of myMethod1 () is void, the return statement is optional.

public void myMethod1() { } 

myMethod2 () shows the optional return statement that correctly doesn't return anything.

public void myMethod2() { return; } 

myMethod3() is a valid method with a String return type and a return statement that returns a String.

public String myMethod3() { return ""; } 

myMethod4() doesn't compile because the return statement is missing.

public String myMethod4() { }  // DOES NOT COMPILE 

myMethod5() doesn't compile because the return type is missing.

public myMethod5() { }  // DOES NOT COMPILE 

myMethod6() has a return statement, but it doesn't always get run. If a is 5, the return statement doesn't get executed. myMethod6() requires a String to be returned.

String myMethod6(int a) { if (a == 4) return ""; }  // DOES NOT COMPILE 

When returning a value, it must be assignable to the return type.

long1 method returns a long type which cannot be assigned to int type.

int integer1() { 
  return 9; 
} 
int long1() {
  return 9L; // DOES NOT COMPILE 
} 

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