// Purpose. Strategy design pattern

// 1. Define the interface of an interchangeable family of algorithms
// 2. Bury algorithm implementation details in derived classes
// 3. Derived classes could be implemented using the Template Method pattern
// 4. Clients of the algorithm couple themselves strictly to the interface

interface Strategy { public void solve(); } // 1. Define the interface
// of the algorithm
abstract class TemplateMethod1 implements Strategy { // 2. Bury implementation
public void solve() { // 3. Template Method
start();
while (nextTry() && ! isSolution())
;
stop();
}
protected abstract void start();
protected abstract boolean nextTry();
protected abstract boolean isSolution();
protected abstract void stop();
}

class Impl1 extends TemplateMethod1 {
private int state = 1;
protected void start() { System.out.print( "start " ); }
protected void stop() { System.out.println( "stop" ); }
protected boolean nextTry() {
System.out.print( "nextTry-" + state++ + " " );
return true; }
protected boolean isSolution() {
System.out.print( "isSolution-" + (state == 3) + " " );
return (state == 3);
} }

abstract class TemplateMethod2 implements Strategy { // 2. Bury implementation
public void solve() { // 3. Template Method
while (true) {
preProcess();
if (search()) break;
postProcess();
} }
protected abstract void preProcess();
protected abstract boolean search();
protected abstract void postProcess();
}

class Impl2 extends TemplateMethod2 {
private int state = 1;
protected void preProcess() { System.out.print( "preProcess " ); }
protected void postProcess() { System.out.print( "postProcess " ); }
protected boolean search() {
System.out.print( "search-" + state++ + " " );
return state == 3 ? true : false;
} }

public class StrategyDemo { // 4. Clients couple strictly to the interface
public static void clientCode( Strategy strat ) { strat.solve(); }
public static void main( String[] args ) {
Strategy[] algorithms = { new Impl1(), new Impl2() };
for (int i=0; i < algorithms.length; i++)
clientCode( algorithms[i] );
} }

// start nextTry-1 isSolution-false nextTry-2 isSolution-true stop
// preProcess search-1 postProcess preProcess search-2