org.glassfish.pfl.basic.contain.Display Maven / Gradle / Ivy
/*
* Copyright (c) 2008, 2018 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
/*
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*/
package org.glassfish.pfl.basic.contain;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/** Supports a Display as typically found in Lexical scoping.
* Upon entering a scope, a new environment is available for
* binding keys to values. Exiting a scope remove the top-most
* environment. Lookup searches from the top down to find the
* value for the first matching key.
*
* @param The type of the Key
* @param The type of the Value
* @author ken
*/
public class Display {
private List> display = new ArrayList>() ;
public void enterScope() {
display.add( new HashMap() ) ;
}
public void exitScope() {
if (display.isEmpty()) {
throw new IllegalStateException( "Display is empty" ) ;
}
display.remove( display.size() - 1 ) ;
}
public void bind( K key, V value ) {
if (display.isEmpty()) {
throw new IllegalStateException( "Display is empty" ) ;
}
display.get( display.size() - 1 ).put( key, value) ;
}
public void bind( Map bindings ) {
if (display.isEmpty()) {
throw new IllegalStateException( "Display is empty" ) ;
}
display.get( display.size() - 1 ).putAll( bindings ) ;
}
public V lookup( K key ) {
V result = null ;
for (int ctr=display.size()-1; ctr>=0; ctr-- ) {
result = display.get( ctr ).get( key ) ;
if (result != null) {
break;
}
}
return result ;
}
}